In a mixing bowl, combine the egg yolks and 25g of granulated sugar. Whisk until pale and creamy, about 3-4 minutes.

In a saucepan over medium heat, combine the heavy cream, strongly brewed coffee, vanilla extract, and a pinch of salt. Stir until bubbles form but do not boil.

Gradually pour the warm cream mixture into the whisked egg yolks while whisking continuously. Return the mixture to the saucepan and cook over low heat for about 5 minutes until thickened.

Remove from heat and let the custard cool completely at room temperature or refrigerate for 15-20 minutes.

Beat the egg whites with the remaining 75g of sugar and cream of tartar until stiff peaks form and glossy. This creates the meringue.

Gently fold the meringue into the cooled custard in two additions, maintaining airiness.

Portion the mousse into 4-5 dessert cups, covering them with plastic wrap. Chill in the refrigerator for 1-2 hours.

After chilling, dust with cocoa powder and garnish with coffee beans before serving.