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Preheat oven to 350 degrees. Grease and flour a Bundt pan; set aside.
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Separate eggs into two small bowls; set aside.
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Beat butter and sugar in large bowl fitted with paddle attachment until light and fluffy.
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Add poppy seed filling and beat until blended. Add in egg yolks, one at a time, beating well after each addition.
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Add vanilla and sour cream and beat until just blended.
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Mix in baking soda and salt. Add flour, a half-cup at a time, beating well after each addition.
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Beat egg whites in separate bowl with electric mixer until stiff peaks form. If you have a hand mixer, you can use this; I always just use my Kitchen Aid fitted with the whisk attachment and hold the glass (non-Kitchen Aid) bowl in place. It seems to work just fine!
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Fold beaten egg whites into batter. Spread evenly into prepared pan.
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Bake approximately 1 hour, until knife inserted in center comes out clean. Cool in pan on wire rack 10 minutes. Remove from pan and cool completely on rack.
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After cake has cooled, bring 1/4 cup water to a boil in small saucepan. Slowly add powdered sugar, whisking well, until mixture reaches a smooth glaze consistency. Add in meringue powder and remove from heat.
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Keep stirring with whisk, as glaze will cool and harden fairly quickly. Transfer glaze to liquid measuring cup or small pitcher, if desired, then drizzle over cake.