Preheat oven to 325 degrees F. Spray a 10 inch tube pan or 12 cup Bundt pan with flour-added baking spray.Sift together dry ingredients; Set aside.in the bowl of a stand mixer, beat butter and 2 1/2 cups (500g) of sugar until light and creamy. For best results, beat for a long time — about 8 minutes, adding the sugar gradually. Beat in egg yolks one at a time.Beat in extracts.
Remove bowl from stand and sift in the flour mixture 1/2 cup at a time, alternating with the sour cream. Stir or fold with a heavy duty scraper to mix.In a clean metal bowl, beat the egg whites until soft peaks form. Gradually beat in the remaining 1/2 cup (100g) of sugar until shiny, soft, billowy peaks. Do not overbeat. Fold into batter.
Bake for 50-75 minutes, until cake tests done. Alternately, you can bake the cake at 300 degrees F. for about 2 hours. This is my latest favorite way to bake it — slow and low.