Whisk together brown sugar, cocoa powder, cornstarch and salt in a medium saucepan, then gradually whisk in the milk and 1/2 cup heavy cream. Bring to a low boil, whisking constantly, and simmer and whisk until pudding is thickened, about 3 to 5 minutes. Remove from heat.
In a small bowl, beat egg yolk. Add a bit of the hot chocolate pudding and whisk to incorporate. Add the yolk and pudding back to the pudding pot and cook over low heat for 2 to 4 minutes, whisking constantly.
Remove from heat and whisk in chocolate and vanilla extract until chocolate is completely melted. The pudding will be the consistency of thick but melty ice cream and will solidify more in the refrigerator as it cools.
Divide between small cups, cover with plastic wrap and place in the refrigerator for at least 4 hours before serving.
Just before serving, in a medium bowl whisk together heavy cream and powdered sugar until thickened and holds its shape on a spoon. Dollop on pudding. Serve with ripe figs or raspberries and enjoy!