In a clean and dry mixing bowl, whisk the egg white until stiff peaks form. This should take about one minute with an electric mixer. Once it's whipped, set it aside; this will give our waffles a light and airy texture.
In another mixing bowl, combine all other ingredients: peanut butter, melted butter, whey protein powder, almond milk, granulated sweetener, baking powder, and vanilla extract. Blend them until smooth. The batter should be well-mixed without any lumps.
Next, gently fold the whipped egg whites into the yolk mixture using a spatula. Be careful to maintain the air bubbles; this step is crucial for fluffy waffles.
Now, preheat your mini waffle maker. Brush both surfaces with a little melted butter or oil to prevent sticking.
Spoon about two tablespoons of the batter into the waffle maker. Close the lid and cook until the waffles are golden brown. This usually takes just a few minutes.
Once cooked, carefully remove the waffle with a fork and let it cool on a wire rack. This prevents the waffles from becoming soggy.
Continue using the batter, brushing more butter onto the waffle maker as needed until you’ve used it all up. This recipe typically yields four mini waffles.