Line a 17x12 rimmed baking sheet with parchment paper. Preheat oven to 365°F at step 4.
Separate egg yolks and egg whites. In a large bowl, add the egg whites. Beat on high speed until soft peaks form, 2-3 minutes. Slowly add sugar, beat until stiff peaks form, 2-3 minutes.
In a separate bowl, beat egg yolks and sour cream for 1 minute. Pour into egg whites bowl, beat on medium speed until egg yolks are incorporated.
In a bowl, combine flour, baking powder, and poppy seed. Add to the egg mixture. Mix for a few seconds on low speed until flour is combined. Turn off mixer and with a spatula, gently mix to make sure the flour is well incorporated. Don't overbeat or else the mixture will flatten. Pour mixture into baking sheet, spread evenly.
Bake 12 minutes or until toothpick comes out clean if inserted in the center of the cake. Slightly cool.
Run a knife along edges of cake to loosen from sheet. Remove cake roulade from baking sheet, cover with a kitchen towel and roll roulade up while it's still warm but not hot. Set aside to cool completely.