Place a small saucepan over very low heat and add the chocolate. When the chocolate starts melting, pour in the maple syrup and the coffee.
1 cup dark 56% to 80% semi-sweet chocolate, broken into pieces, at room temperature, plus extra for garnish, 1 tablespoon maple syrup, ½ cup brewed coffee
Stir continuously until the ingredients are well combined and all the chocolate is completely melted—you should have a shiny dark chocolate paste. Remove from heat; reserve.
Using a stand mixer or electric hand mixer on medium to high speed, beat the egg whites until stiff peaks form (4 to 5 minutes).
4 egg whites at room temperature
Use a (rubber) spatula to scrape the reserved chocolate mixture from the pan and add it to the beaten egg whites in thirds.
At first, gently fold in the mix for a few seconds, then use a regular whisk and gently stir until everything is thoroughly blended and you have a beautiful brown mousse. Note: don't overmix here. It is important to work quickly but not vigorously, so the peaked egg whites won't deflate too much.
Divide the mousse evenly into 4 small cups, ramekins, or serving bowls.
Chill in the refrigerator for at least 30 minutes (I usually let it sit for 2 hours, or you can let it sit overnight.)
When ready to serve, garnish with a raspberry and extra chocolate shavings.
Fresh or frozen raspberries/blackberries to garnish