1. Heat the oven to 350 degrees. Generously coat a large flute pan with cooking spray on the fluted center and bottom only, but not on the outer sides of the pan.
2. In the bowl of a stand mixer, combine the egg whites, cream of tartar, xanthan gum, guar gum, baking powder, stevia and both extracts.
3. Beat on low for 30 seconds, then increase mixer to high and beat until very stiff peaks form, about 4 minutes. The mixture will be airy, voluminous and quite thick.
4. Into a small bowl, sift together the protein powder, almond flour and powdered egg whites. Sprinkle half of the dry ingredients over the egg whites. Run the mixer at medium for 5 seconds, or just until the dry ingredients are incorporated. Sprinkle the remaining dry ingredients over the egg whites and mix again just to incorporate.
5. Increase mixer speed to high and run for 5 more seconds.
6. Use a silicone spatula to scrape the sides of the bowl and gently fold the mixture together once or twice. Transfer half the mixture to the prepared pan, then use the spatula to smooth the top. Repeat with the remaining mixture. Firmly tap the pan on the counter to help eliminate air bubbles.
7. Bake for 35 minutes. Remove the pan from the oven and overturn the pan and cool upside down. When cool, to release the cake, run a paring knife along the outside of the pan.
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