Preheat your oven to 350°F. While it heats, line an 8x8 inch baking dish with parchment paper or lightly grease it with cooking spray. This prevents sticking and makes removal easier. Set the prepared pan aside while you mix the batter.
In a medium mixing bowl, combine the room temperature egg, greek yogurt, cocoa powder, protein powder, coconut sugar, and baking powder. Stir vigorously until you have a smooth, thick batter with no lumps—this usually takes 1-2 minutes of mixing. The room temperature egg helps the batter emulsify properly and creates a better texture. I like using thick greek yogurt like Fage Total 0% because it gives these brownies a fudgy, dense crumb that regular yogurt just can't match.
Pour the batter from Step 2 into your prepared pan, spreading it evenly with a spatula. The batter will be thick and dense, which is exactly what you want. Bake for 20-25 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs (not wet batter). Don't overbake—these brownies should be fudgy and moist, not cake-like.
Remove the brownies from the oven and let them cool in the pan for at least 15 minutes before cutting. This cooling time allows them to set properly and makes them easier to slice cleanly. For an extra flavor boost, I like to lightly dust the warm brownies with a tiny pinch of sea salt—it enhances the chocolate flavor and adds a subtle sophistication.