Use a stand or electric mixer to beat the egg whites on medium-high speed until foamy, about 30 seconds.
Add almond and vanilla extracts. Continue to beat until soft peaks form.
Slowly beat in sweetener, 1 tablespoon at a time, until soft glossy hills form.
Slowly beat in tapioca starch, ¼ cup at a time, until smooth.
Pour the batter into a 12-inch greased bundt or tube pan. Smooth the top of the batter with a spatula.
Bake for 35-40 minutes. The cake should rise significantly and the top should be a medium brown.
Immediately invert the cake pan so air can circulate around the pan as it cools. If the pan does not have legs, hold the pan above the counter, using a wine bottle or can. Cool for about 2 hours or until completely cooled.
Use a knife to carefully cut around the sides and the inner tube of the pan to release the cake. Slice around the inner tube of the pan. Carefully release the cake.
Slice the cake into 12 pieces using a serrated knife.
Serve with berries and whipped cream.
When separating your egg whites be sure to use a very clean dry bowl to not get any yolk in your whites. This will prevent the whites from whipping into peaks.