Prep your chocolate. Chop the dark chocolate and melt it gently in the microwave in 20–30 second bursts, stirring between each, or over a double boiler.
Let it cool for 5 minutes so it’s warm but not hot.
Choose your base. Add silken tofu, Greek yogurt, or whipped cottage cheese to a blender or food processor. If using cottage cheese, blending is key to get it perfectly smooth.
Add dry ingredients. Sprinkle in cocoa powder and a pinch of salt. If you’re using espresso powder or protein powder, add it now.
Blend with flavorings. Add vanilla and your sweetener of choice.
Blend until smooth and creamy, scraping down the sides as needed.
Stream in the chocolate. With the blender running on low, pour in the melted chocolate. It will thicken the mixture and give it a glossy, mousse-like consistency.
Adjust consistency. If it’s too thick, add milk 1 tablespoon at a time and blend until it’s airy and silky. Taste and adjust sweetness.
Chill to set. Spoon into serving glasses or ramekins.
Cover and refrigerate for at least 1–2 hours. The texture will firm up into a classic mousse.
Garnish and serve. Top with berries, shaved chocolate, or a sprinkle of cacao nibs. Serve cold.