Unfold puff pastry and cut into 3 equal pieces along the fold. Roll each sheet out slightly. Using a 2 1/2-inch cutter, cut 4 rounds out of each strip, giving you 12 rounds total. Using a 1 1/2-inch cutter, press into each round, making a solid indentation without cutting completely through the pastry.
Place rounds on a baking sheet lined with parchment paper and top with a baking rack. This will keep the rounds uniform and even as they puff up during baking. Bake until rounds are golden, about 20 to 25 minutes. Transfer to a rack to cool slightly, about 5 minutes.
Using the tip of a spoon, carefully remove the inner circle of the puff pastry creating a nest. Fill each nest with 1 teaspoon of the bacon bits and top with 2 teaspoons of the mascarpone. Garnish with grape halves and a sprinkle of parsley. Serve on individual plates or a serving platter.