Preheat the oven to 425 degrees F.
Zest 2 of the lemons and set the zest aside.
Cut the remaining peel and pith away from the lemons, and dice the flesh into ¼” pieces.
Place in a small bowl, sprinkle with 1 tablespoon of the sugar, stir to coat, and set aside.
In a large mixing bowl, place the flour, remaining sugar, baking powder, salt, and reserved lemon zest, and stir to combine.
Cut in the mascarpone and butter until the mixture resembles coarse meal.
Add the lemons and milk, and stir until just barely combined.
Gather the dough into a ball, place on a parchment-lined baking sheet, and press to a thickness of about 1 inch.
Cut the scones into 6 equal wedges, and space them approx. 1 inch apart.
Sprinkle with clear sparkling sugar.
Bake for 16-18 minutes, or until slightly golden on the tops and around the edges.