Whip the Cream: In a medium bowl, use a hand mixer to whip the heavy cream until stiff peaks form (about 2–3 minutes). Be careful not to overwhip—it should be smooth and billowy. Cover and refrigerate to keep it chilled.
Whip the Egg Yolks and Sugar: In a separate bowl, combine the egg yolks and granulated sugar. Use a hand mixer to whip until the mixture is pale yellow and slightly thickened (about 2 minutes). Set aside.
Set Up the Double Boiler: Fill a medium saucepan with a few inches of water and bring to a gentle boil. Place a heat-safe metal or glass bowl over the saucepan, ensuring the bottom doesn’t touch the water. This is your double boiler!
Melt the Chocolate Mixture: In the bowl of the double boiler, combine the bittersweet chocolate, butter, water, and espresso powder. Stir frequently with a whisk until the chocolate is fully melted and smooth. Remove the bowl from the heat.
Temper the Eggs: Slowly add about ¼ of the hot chocolate mixture to the egg yolk/sugar mixture, whisking constantly. This tempers the eggs to prevent scrambling. Once combined, pour the tempered egg mixture back into the remaining chocolate mixture in the bowl. Add the vanilla extract and mix well.
Cook the Chocolate Mixture: Return the bowl to the double boiler and cook over low heat, stirring constantly, until the mixture thickens slightly (about 3–5 minutes). It should coat the back of a spoon. Remove from heat and let cool to room temperature (about 15 minutes).
Whip the Egg Whites: In a clean, dry bowl, use a hand mixer to whip the egg whites until stiff peaks form (about 2–3 minutes). They should be glossy and hold their shape.
Fold It All Together: Gently fold the cooled chocolate mixture into the whipped egg whites using a spatula. Work carefully to keep the mixture light and airy. Next, fold in the chilled whipped cream until the mousse is smooth and evenly combined.
Chill the Mousse: Divide the mousse into individual serving dishes (like canning jars) or keep it in one large bowl. Cover with plastic wrap and refrigerate for at least 6 hours, or overnight, to set.
Serve & Enjoy: Serve chilled with a dollop of whipped cream, fresh berries, or a dusting of powdered sugar. Enjoy the melt-in-your-mouth magic!
Notes
Make-Ahead: This mousse is perfect for preparing a day in advance. It needs time to chill, so plan accordingly.
Storage: Store covered in the fridge for up to 3 days. It’s best enjoyed fresh but holds up well.
Egg Safety: If you’re concerned about raw eggs, use pasteurized eggs for peace of mind.
Serving Size: This recipe makes about 4 generous servings or 6 smaller ones. Adjust based on your crowd!