Brew 30 g of Robusta ground coffee with 120 ml of hot water using a phin filter or espresso machine. You need a concentrated liquid, dark and slightly syrupy. Let it cool to room temperature.

Stir in the sweetened condensed milk, vanilla extract, and salt until fully combined. Taste it. It should be bitter, sweet, and strong.

Sprinkle the powdered gelatin over 3 tbsp of cold water in a small bowl. Let it sit for 5 minutes until it swells into a soft, spongy mass.

Warm the bloomed gelatin gently in a small saucepan over low heat, stirring until it turns completely clear and liquid with no lumps. Remove from heat immediately.

Stir the dissolved gelatin into the cooled coffee and condensed milk mixture. Mix well and set aside to cool slightly, about 5 minutes.

Whip 200 ml of the heavy cream in a chilled mixing bowl using an electric mixer until stiff peaks form. The cream should hold its shape when you lift the beaters.

Fold the whipped cream into the coffee-gelatin mixture in three additions, using a rubber spatula and gentle sweeping motions. Stop as soon as no white streaks remain. Don't stir or beat.

Divide the mousse evenly between 4 glass cups. Tap each cup lightly on the counter to release any large air bubbles.

Refrigerate uncovered for 30 minutes until the surface is firm enough to hold the topping, then cover loosely with plastic wrap and chill for at least 90 more minutes, or up to 24 hours.

Whip the remaining 100 ml of cream with 2 tbsp of powdered sugar until soft peaks form. Spoon or pipe a small cloud of whipped cream on top of each set mousse cup.

Dust lightly with cocoa powder through a fine-mesh sieve if using. Serve immediately, straight from the fridge.