Preheat the oven to 350°F (175°C). Grease a small baking pan (about 9x9 inches).
In a mixing bowl, whisk together flour, sugar, cocoa powder, baking powder, and salt.
Add milk, melted butter, vanilla extract, and egg, and mix until smooth.
Pour the batter into the prepared baking pan and bake for 18–22 minutes, or until a toothpick comes out clean. Let the cake cool completely.
For the mousse: Melt the semi-sweet chocolate in a microwave-safe bowl and let it cool.
Whip heavy cream, powdered sugar, and vanilla extract until soft peaks form.
Gently fold the melted chocolate into the whipped cream to create a smooth mousse.
For the whipped cream topping: Whip heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
Once the cake has cooled, cut it into small rounds to fit your dessert cups.
Assemble the Dolcini by layering the chocolate cake at the bottom, followed by a layer of chocolate mousse, and then the whipped cream topping. Repeat the layers as needed.
Garnish with chocolate shavings, cocoa powder, or mini chocolate chips.
Refrigerate for at least 1 hour to allow the layers to set.
Serve chilled and enjoy!