Heat the oven to 350°F and line 12 muffin cups with paper liners. Stir the espresso powder into the hot water and let it cool slightly.
Whisk the almond flour, cocoa powder, allulose, baking powder, and salt together. Add the eggs, melted butter, vanilla, and dissolved espresso, then whisk just until the batter is smooth.
Divide the brownie batter among the muffin cups and bake for 12 to 15 minutes, until the tops are set but the centers remain fudgy. Cool completely.
Stir the brewed coffee with the powdered allulose. Brush about 1 teaspoon of the sweetened coffee over each cooled brownie cup so the tops become moist without turning soggy.
Beat the mascarpone, cream cheese, powdered allulose, and vanilla until smooth. Add the cold heavy cream and beat just until the mixture becomes thick and fluffy.
Spoon or pipe the mascarpone cream over the brownie cups, dust lightly with cocoa powder, and refrigerate for at least 1 hour before serving.