Heat the oven to 350F. Line an 8x8 pan with parchment paper. Spray with cooking oil.
Whisk the blended cottage cheese, maple syrup, peanut butter, and vanilla until smooth.
In a separate bowl, combine oat flour, cocoa, baking powder, and salt. Combine the wet and dry ingredients; it will form a very thick batter.
Mix the filling ingredients and leave for 2 to 3 minutes until thick and dough-like.
Spread two thirds of the batter over the base of the pan. Level it out.
Flatten spoonfuls of the filling between your fingers and arrange them over the batter, piece by piece.
Stir 2 tbsp milk into the remaining one third of the batter to loosen it, then spread it gently over the filling to seal.
Cover with chopped chocolate.
Bake 30 to 34 minutes, checking from 28. Judge by the brownie edges, not the peanut butter center: top set, edges cooked, a tester inserted near the edge should come out with moist crumbs.
Cool completely in the pan, then chill 30 to 60 minutes before slicing.