Add cottage cheese, (optional) collagen, and cocoa powder to a high-speed blender. Blend until silky smooth, scraping the sides as needed.
Melt dark chocolate chips or bar in a microwave by adding a splash of milk to the bowl and microwave for 30 seconds, take out and stir, then return to the microwave for another 20 seconds. Take out and stir until all melted and smooth.
Pour in the melted chocolate and add vanilla extract. Blend again for a creamy base.
Taste: if the chocolate flavor is perfect, move on! If sweeter mousse is desired, add monk fruit sweetener, liquid stevia, or maple syrup, blend, and taste again.
For a creamier mousse, add Greek yogurt or cream cheese and blend once more.
Spoon cottage cheese mixture into serving jars or an airtight container. Chill for 30 minutes or cover with plastic wrap for later (best results).
Top with fresh fruit, chia seeds, or extra chocolate chips for a delicious sweet treat.