Preheat oven to 325 F. Then sift together almond flour, coconut flour, salt, and xanthum gum. It’s very important that you sift them, since this is a delicate cake.
Put egg whites and cream of tartar in a clean mixing bowl and mix on low until frothy (about a minute). Then increase speed to medium-high to form soft, billowy egg whites.
While the mixer is running and when large bubbles stop appearing close to the edges, begin adding the powdered sweetener – one tablespoon at a time since this ensures a gorgeous meringue.
Keep mixing until you have a shiny meringue that forms soft peaks when the beater is lifted, about 5-6 minutes.
When soft peaks have formed, stop the mixer and slowly add vanilla, orange extract, orange juice and orange zest.
Then turn the beater on again just long enough for the ingredients to mix.
Sift the flour mixture in 3 installments into the egg whites, using a spatula each time to gently fold in the flour. With your spatula, cut through the middle, then sweep your spatula along the side of the bowl. Turn the bowl and keep repeating.
Taste the fluffy meringue. If it needs a touch more sweetener, then gently sift it in.
Slowly spoon meringue into ungreased angel food cake pan.
Bake 45-55 minutes until golden brown on top.
Immediately flip cake onto its feet. Allow it to cool upside-down upwards of 3 hours so it FULLY cools.
To remove cake, firstly, run a knife (a thin knife) along the outside of the cake using a gentle up and down motion. Also run it along the center ring. Then use the tube to pull the cake out of the pan. Put it on a work surface. Use a chef's knife to cut the bottom free. Invert it and flip onto a plate.
The cake will be upside down. Flip it right-side up, if desired.