Preheat oven to 350°F (175°C).
In a bowl, whisk together the egg, egg whites, Greek yogurt, melted coconut oil, and vanilla.
Add the dry ingredients and mix until smooth.
Pour batter into a greased or lined 8×8-inch or 6x6-inch pan and spread evenly.
Bake for 15–20 minutes for 8x8 or 20-25 for 6x6, taking them out slightly underdone for the fudgiest texture.
Let cool, then cut into 16 brownies (4×4) or into 9 (3x3) and enjoy!
