Pre-heat your oven to 350°F. Line an 8x8 brownie pan with parchment paper for easy removal and set aside.
Add the cottage cheese to a food processor or blender and pulse until completely smooth with no lumps remaining. Transfer to a large bowl and add the peanut butter and all remaining dry ingredients. Using a fork or silicone spatula, mix the brownie batter until fully combined.
Scoop the batter into your prepared pan and use the back of a spatula to press it down evenly across the pan. Bake for 15-20 minutes for fudgy brownies, or 25 minutes for a cakey texture.
Once baked, leave the brownies in the pan to cool completely for best results.
Add the chocolate chips and butter to a small heatproof bowl. Heat the milk until steaming then pour it over the chocolate and butter. Let it sit for 1 minute, then slowly whisk until fully incorporated.
Pour the chocolate ganache evenly over the cooled brownies. Scatter rainbow sprinkles over the top. Refrigerate for at least 1 hour to set before slicing.
