Three layers of chocolate for the chocolate lovers out there.
Prepare chocolate cake layer:
Preheat your oven to 325 degrees F.
Butter a 9" round spring form pan. Set aside.
Separate egg yolks and whites. Set aside.
In a double boiler, melt chocolate, butter and espresso powder, whisking until smooth. Cool slightly for 5 minutes.
Add egg yolks and vanilla extract and whisk until well combined.
In a large mixing bowl, whip egg whites with salt for 30 seconds, or until frothy. Add half of the brown sugar, sprinkling it over the frothy whites. When the sugar is well mixed in, add the remaining half. Whip until soft peaks form.
Gently whisk in 1/3 of whipped whites to chocolate mixture.
Whisk just until the mixture lightens in color. Switch to a rubber spatula and gently fold in the rest of whites, until no streaks remain.
Carefully pour the chocolate mixture into prepared pan. Smooth the top out.
Bake the cake for 15 to 18 minutes or until the center springs back when pressed down.
Leave the cake in the spring form and cool completely, at least 1 hour.
Place chips and cream in a glass bowl.
Melt in the microwave or double boiler, stirring often.
Whisk till totally smooth. Let cool to thicken.
Once cake is cool, spread a thin layer of ganache over the cake.
Chocolate Mousse Layer:
In a small bowl, mix together cocoa powder and hot water. Set aside to cool slightly.
In a double boiler, melt chocolate. Cool 3 to 5 minutes.
In a large mixing bowl of a stand mixer, whip cream, sugar and salt at medium speed. Whip for 30 seconds. It should slightly thicken. Increase the speed to high and whip the cream until soft peaks form. Set aside.
Whisk cocoa powder mixture with melted chocolate until smooth.
With whisk, fold in 1/3 of the whipped cream into chocolate mixture to lighten it. Switch to a rubber spatula and gently fold in the rest of the whipped cream, until no streaks remain.
Spoon the mousse over cooled cake. Tap the form on your countertop 3 times to get rid of any air bubbles. Smooth the top with a spatula.
Wipe the inside of the pan with a paper towel from any mousse smudges. Refrigerate the cake for at least 15 minutes so the mousse can set.
Once set, use a spatula to pour the remaining ganache over the mousse and smooth top.
Refrigerate and let set for 1 hour in fridge before cutting.