In a small bowl, whisk together ¼ c milk, eggs, espresso, and sugar.
Place the bread cubes in a medium bowl and pour the egg mixture over the cubes. Mix to coat the bread with the egg mixture and set the mixture aside for the bread cubes to soak up the liquid while your oven preheats.
Preheat your oven to 375F.
Place the soaked bread cubes into a greased, 3 c ramekin or oven-safe dish. Place the ramekin on a baking sheet (to catch any bubble over) and bake for 25-30 minutes, until the pudding has set and a knife inserted into the center comes out moist, but without any crumbs attached.
Place the ramekin on a wire rack to cool slightly.
In a medium bowl, whip the mascarpone with 2 tablespoon milk and powdered sugar, until light and fluffy.
Gently, remove the bread pudding from the baking dish and place on a serving plate. Top with mascarpone topping and dust with cocoa powder.