Preheat oven to 350°F (175°C) and line an 8×8 inch baking pan with parchment paper, leaving overhang on sides.
In a large bowl, whisk together flour, cocoa powder, baking soda, and salt until well combined.
Add granulated sugar, brown sugar, cottage cheese, Greek yogurt, eggs, melted butter, and vanilla extract to the dry ingredients.
Use a whisk or electric mixer to beat everything together until just combined. Do not overmix.
Pour batter into prepared baking pan and spread evenly with a spatula.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached.
Let brownies cool completely at room temperature in the pan on a wire rack for at least 1 hour before lifting out using parchment paper overhang and cutting into squares.
If using frosting, beat softened cream cheese, powdered sugar, and milk together until smooth. Spread over cooled brownies before cutting.
Notes
Do not overmix the batter as this can make brownies tough. Mix until just combined.
Cottage cheese and Greek yogurt should be at room temperature for smoothest batter.
For extra rich flavor, use dark cocoa powder.
Chill brownies in refrigerator for 1 hour before cutting for cleanest slices.