Preheat oven to 350°F (175°C). Grease and line a 7" (18 cm) springform pan with parchment (baking paper).
Blend cottage cheese, eggs, peanut butter, and sweetener until smooth.
In another bowl, whisk flour, cocoa, baking powder, and coffee (if using).
Combine the wet and dry ingredients until just mixed (don’t overmix).
Pour into the prepared pan and smooth the top.
Bake for 25-30 minutes, until a toothpick comes out mostly clean (a few moist crumbs are fine).
Allow the cake to cool in the pan for 10 minutes. Then, turn out onto a wire rack and let it cool completely.