Preheat the oven to 350°F (175°C).
In a bowl, whisk together flour, baking soda, and salt; set aside.
In a large bowl, beat the softened butter, granulated sugar, and brown sugar until creamy and well-combined.
Add the egg and vanilla extract to the butter mixture, and mix until fully incorporated.
Gradually blend the dry ingredients into the wet mixture until just combined.
Scoop tablespoon-sized portions of dough into a greased muffin tin, pressing the dough down slightly to create cups.
Bake for 10-12 minutes, until the edges are golden brown.
Remove from the oven and allow to cool completely in the tin before removing.
In a separate bowl, whip the heavy cream until stiff peaks form; set aside.
In another bowl, combine mascarpone, powdered sugar, and cooled coffee, mixing until smooth.
Fold the whipped cream into the mascarpone mixture gently.
Spoon or pipe the mascarpone filling into the cooled cookie cups.
Dust with cocoa powder just before serving for that classic tiramisu look.
