Add the Greek yogurt and cottage cheese to a high-speed blender or food processor, making sure both are well chilled. Blend on medium to high speed until the mixture becomes completely smooth and creamy, stopping once or twice to scrape down the sides if needed. Take your time with this step — fully breaking down the cottage cheese is what creates that true mousse-like texture instead of a grainy or lumpy finish.

Once the base is silky, add the unsweetened cocoa powder, your chosen sweetener, and the vanilla extract. Blend again until the cocoa is fully incorporated and the mixture turns a deep, rich chocolate color. Pause to taste at this stage and adjust sweetness if needed, blending briefly after each adjustment so the flavor stays balanced and smooth.

Add the protein powder along with a small amount of milk or milk alternative. Blend gently at first, then increase speed until everything is fully combined and creamy. If the mousse feels too thick, add a little more milk a tablespoon at a time, blending between additions until you reach a thick but spoonable consistency that holds its shape.

Transfer the finished mousse into individual serving containers or small jars and smooth the tops with a spoon or spatula. Refrigerate for at least 30 minutes before serving, allowing the mousse to set and the flavors to deepen. Once chilled, it will be thicker, more cohesive, and perfectly creamy — ready to enjoy right away or store for later.