This is an unusual one layer cake. It can be used for Passover or as an intriguing dessert or coffee cake at any time. I got this from my friend Irene Lawrence, and artist who always knows exotic things.
Grease 9" Springform pan and line bottom with parchment.
Preheat oven to 300 F.
Using a coffee grinder, grind the poppy seeds in batches for about 20 seconds. The seeds will become sticky.
Combine with potato starch in large bowl.
Beat egg yoks until slightly thickened. Slowly add sugar and vanilla. Slowly pour in butter, then add poppy seed mixture. Beat until combined.
Using clean bowl and whisk, beat egg whites until they form soft peaks. Fold them in batter and pour into prepared pan. Bake for 50-60 minutes until toothpick inserted in center comes out fairly dry. Cool on wire rack for an hour before unmolding. Dust with powdered sugar or cocoal before serving.