Preheat the oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper, leaving edges overhanging.

Drain the cottage cheese in a fine mesh sieve or cheesecloth for at least 10 minutes to remove excess liquid.

In a medium bowl, whisk together the eggs and sweetener until smooth and slightly pale.

Add the drained cottage cheese and melted coconut oil, blending until well combined. Optionally pulse in a blender for a smoother texture.

In a large bowl, sift together the cocoa powder, protein powder, oat flour, baking powder, espresso powder (if using), and salt.

Carefully fold the wet ingredients into the dry ingredients until just combined; do not overmix.

Pour the batter into the prepared pan and smooth the top with a spatula.

Add any desired mix-ins, folding or swirling gently.

Bake for 22-25 minutes, checking at 20 minutes. Insert a toothpick; it should come out with a few moist crumbs.

Allow brownies to cool completely in the pan on a wire rack.

Refrigerate for at least one hour before slicing.