1. In a large mixing bowl and using an electric mixer, beat the egg whites and salt on high speed until stiff peaks form. Set aside.
2. In a second large bowl, whisk egg yolks, soy milk, mascarpone, butter, sweetener, and vanilla. Add the coconut-flax flour blend, protein powder, cocoa powder, and baking powder and stir to combine.
3. Add ¼ cup beaten egg whites to the egg yolk mixture. Using a rubber spatula, fold in the egg whites and all of the flour until just combined, about 8 turns, forming a sticky mass. Fold in another ¼ cup egg whites until the mixture becomes lighter, an additional 4–5 turns. Finally, fold in the remaining egg mixture. There will be small lumps. Don’t overmix.
4. Heat a waffle iron according to the manufacturer’s instructions and mist with cooking spray. Add ½ cup batter and spread it evenly with the back of a spoon. Cover and cook 2–3 minutes or until the waffle is firm and light brown. Repeat with remaining batter and serve immediately. Or cool to room temperature, double-wrap in plastic wrap, and freeze.