Cut the avocados in half, remove the pits, and scoop the flesh into a food processor or high-powered blender.
Add the cocoa powder, sweetener, almond milk, vanilla extract, sea salt, and espresso powder if using.
Blend on high for 1-2 minutes, stopping to scrape down the sides as needed, until completely smooth and creamy with no lumps.
Taste and adjust sweetness if needed—remember, the mousse will taste slightly less sweet after chilling.
Divide the mousse among 6 small serving cups or ramekins.
Refrigerate for at least 2 hours to allow the flavors to meld and the mousse to firm up slightly.
Before serving, top with a dollop of sugar-free whipped cream and garnish with fresh raspberries or a sprig of mint for that festive touch!