1. Melt the Chocolate

• Place a heatproof bowl over a saucepan of simmering water (double boiler setup). Add the chocolate, butter, and coffee to the bowl.
• Stir gently until the chocolate and butter are fully melted and the mixture is smooth. Remove from heat and stir in the whiskey. Set aside to cool slightly.

2. Prepare the Egg Yolks

• In another heatproof bowl, whisk the egg yolks with 2 tablespoons of sugar. Place the bowl over the simmering water and whisk until the mixture becomes foamy and slightly thickened (about 2–3 minutes). This step ensures the yolks are gently cooked.
• Remove from heat and mix the egg yolk mixture into the cooled chocolate mixture. Stir until fully combined.

3. Beat the Egg Whites

• In a clean, dry bowl, beat the egg whites with a pinch of salt using an electric mixer until soft peaks form. Gradually add the remaining 2 tablespoons of sugar and continue beating until stiff peaks form.
• Gently fold the egg whites into the chocolate mixture in 2–3 additions, being careful not to deflate the mixture.

4. Whip the Cream

• In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the mousse mixture until fully combined.

5. Assemble and Chill

• Divide the mousse evenly among serving glasses or bowls. Cover and refrigerate for at least 2 hours, or until set.

6. Garnish and Serve

• Just before serving, top each mousse with a dollop of whipped cream. Dust with cocoa powder and sprinkle with chocolate shavings.