Looking for the cutest beach-themed birthday cake? Here’s a super simple step-by-step tutorial on how to make a sandcastle cake that will be a show stopper.

Oh, the cake!

I knew as soon as we decided on a mermaid theme for Annie’s 4th birthday that a sand castle cake would be perfect. I had seen a few really photos on Pinterest, I just couldn’t find any detailed instructions. Since paying hundreds of dollars for a professionally decorated cake was out of the question, I decided to go with plan B: wing it!

I kinda prefer plan B anyways. 😉

Let me just start by saying that I am not a professional baker, or even anything close to it, but what I lack in technical skill I make up for with sheer determination. I’m not going to lie, this cake took forever and a day to make. It was truly a labor of love. But, when all is said and done I was so happy I put in the time because it truly was the focal point of the entire party. Luckily I already had most of the cake ingredients already on hand.

Now, a word about cakes. I am not a professional baker, but I do love to bake. After trying lots of from-scratch cake recipes, I decided that boxed cake mixes are much easier, the texture is often better, and they taste just as good. However, the frosting makes HUGE difference! I almost always make this homemade cream cheese buttercream frosting for my cakes. It is super easy and SO much better than the store-bought stuff!

How to Make a Sandcastle Cake

To make a sandcastle cake, assemble the ingredients: cake mix, eggs, butter, cream cheese, confectioners sugar, oil and graham crackers. Here is what you need:

4 boxes of cake mix
vegetable oil
graham crackers
white or brown sugar
4 sugar cones
5 coconut marshmallows (optional)
1 large batch cream cheese buttercream frosting
candy melts
seashell candy mold & starfish candy mold
9″ square cake pan
2-8″ round cake pans
1-6″ round cake pan
metal cocktail shaker
paper flags
wooden skewers

Pipe melted white chocolate into seashell molds to decorate your sand castle cake.

Step 1: Make the white chocolate seashells & starfish. This is a very easy process! Simply melt the candy melts in the microwave per the bag instructions, then place melted chocolate into a decorating bag, cut off a small hole at the tip, and pipe into the molds. Place in refrigerator to harden for 15-20 minutes, then pop out of the mold. I found that one bag of melts was enough to exactly fill my starfish mold and seashell mold 1 time each.

Toast the coconut for the sand mixture that will cover the outside of your cake.

Step 2: Toast coconut for the sand mixture. Preheat oven to 350 degrees, then lay out several cups of coconut on a baking sheet. Toast in oven for 10-12 minutes until coconut is completely golden brown, stirring several times throughout the process to ensure it is toasted evenly.

Pulse graham crackers and toasted coconut in the food processor to make the sand for your cake.

Step 3:  Make “sand” mixture. Place 2-3 packages graham crackers, toasted coconut, and several cups of white or brown sugar (I used white to get a lighter sand) into a 12 cup food processor and process until mixture resembles a fine sand.

The pulsed graham crackers and coconut should be the consistency of sand when you finish.

Step 4:  Begin making cakes according to the box directions. This process will take a while since you will have to re-use the same pans multiple times. Be sure to grease and flour your pans VERY well each time, especially the cocktail shaker.

You will need an assortment of pans for this cake, including a metal cocktail shaker.

Here is the breakdown of how I baked them:
Box 1 (strawberry): square pan, 6″ round pan, cocktail shaker; reserved small amount in bowl. (See photo below)
Box 2 (strawberry): same as Box 1
Box 3 (coconut): 2 8″ round pans, cocktail shaker filled with excess strawberry from boxes 1 & 2
Box 4 (coconut): square pan, 6″ round pan, cocktail shaker 
Pour the cake batter into each of the pans, including the cocktail shaker. Be sure to tap out any air bubbles before baking.

Tip: Before baking, tap each cake pan firmly on counter several times to release any air bubbles. This will improve your cake’s texture and help it to bake flatter!

When the layers are finished baking allow them to cool on a rack before you build your sandcastle cake.

Step 5: Let all your cake layers cool completely; refrigerate if desired to make them firmer and easier to work with.

Use cones covered in frosting to make the turrets for your castle. Roll them in the toasted coconut and graham cracker crumbs.

Step 6: Make your “turrets” and “battlements” out of sugar cones and marshmallows. First, cut the tip of the cone with a sharp knife enough so that the flags will fit in the hole. Next, smooth frosting over the cone and roll in “sand” mixture until it is completely covered. Repeat process with marshmallows. Set aside or refrigerate until needed.

Insert flags in each cone to go on top of your sandcastle cake.

Step 7:  It is almost time to start assembling your cake, but first you need a base! Cut out a piece of cardboard in a rounded wavy rectangle as shown.

Cut a large cardboard base for your sandcastle cake.

Step 8: Make your “towers.” Cut the bottom of your cooled and chilled cocktail shaker cakes so that the stand up straight. Roll in sand mixture, much like you did with the sugar cones and marshmallows. I found this was easiest to do by sticking a few skewers through the tower so I had something to hold on to. Be sure to get the top as well!

Make your towers by rolling them in the coconut and graham cracker mixture.

Step 9:  It is finally assembly time! If all went according to plan, you should have 3 square layers for your base. Level the layers with a cake leveler if necessary, then place the first layer on your cardboard base, add a thick layer of frosting, the add the second layer, followed by more frosting and the third layer. Frost most of the top and the sides, then carefully add “sand” so that it sticks to the frosting. The goal is to get the whole cake covered with sand.

Layer your sandcastle base and cover the sides with the graham cracker crumbs.

Step 10:  Level the two 8″ round cakes if necessary. Lay the first cake flat side down on top of square cakes. Spread a thick layer of frosting, then add the second 8″ cake flat side up. Spread sides and top edges with frosting, then once again cover the frosting with sand mixture.

Layer the round cakes and cover them with the frosting and graham cracker sand.

Step 11: Repeat this process with the three 6″ round layers. For that section, I found it easiest to assemble the three layers on the counter, then frost and roll the sides in sand like with the tower pieces. Once the top 6″ round layer is in place, push some skewers through the top of cake through all layers to add extra stability, then frost and sand the top of the cake.

Layer the three 6 inch cakes, frost and cover with graham cracker sand.

Step 12:  Once the entire cake has been frosted and sanded it is time to add the towers to the four corners. Use the cocktail shaker to cut out each cake corner, then spread frosting over exposed cake pieces and press tower into place. Add a dollop of frosting to the top of the tower to secure turret in place, and push straw flag through the cone into cake so it stays in place. Cover any cracks or exposed frosting with sand.

Add the cake towers to your sandcastle cake.

Step 13:  Add the battlements to the top of the cake by placing a toothpick in each one and pressing into place.

Insert a toothpick into the battlements and add them to the top of the sandcastle cake.

Step 14:  Add the finishing touches to your cake! Use the seashells and starfish to embellish the top and sides, then, when the cake is in place on the table, use remaining sand to cover the cardboard and make the cake look like it is sitting in a patch of sand. Your guests–and your guest of honor–will be blown away!

Cover the cake and base with the remaining graham cracker sand.

Add white chocolate shells around the sandcastle cake to decorate this beachy treat!


This sandcastle cake was the perfect centerpiece for my daughter's beach-themed mermaid party!

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Looking for the cutest beach-themed birthday cake? Here's a super simple step-by-step tutorial on how to make a sandcastle cake that will be a show stopper.

Ruth Soukup
Ruth Soukup is dedicated to helping people everywhere create a life they love by follwing their dreams and achieving their biggest goals. She is the host of the wildly popular Do It Scared podcast, as well as the founder of Living Well Spending Less® and Elite Blog Academy®. She is also the New York Times bestselling author of six books, including Do It Scared®: Finding the Courage to Face Your Fears, Overcome Obstacles, and Create a Life You Love, which was the inspiration for this book. She lives in Florida with her husband Chuck, and 2 daughters Maggie & Annie.
Ruth Soukup


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