In the bowl of an electric mixer fitted with the flat beater, beat together the mascarpone and lemon curd until fluffy, 2 to 3 minutes. Cover the filling and refrigerate until ready to use.
In a bowl, whisk together the flour, baking soda, baking powder, granulated sugar, salt and lemon zest. In a small bowl, lightly whisk the egg yolks, then whisk in the buttermilk. Whisk the yolk mixture into the flour mixture until well combined; the batter will be lumpy.
In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on high speed until stiff but not dry peaks form, 2 to 3 minutes. Using a rubber spatula, gently stir the egg whites into the batter in 2 additions.
Put 1/2 teaspoons butter in each well of a filled-pancake pan. Set over medium heat and heat until the butter begins to bubble. Pour 1 Tbs. batter into each well. Put 1/2 teaspoons lemon-mascarpone filling into the center of each pancake and top with 1 Tbs. batter. Cook until the bottoms are golden and crispy, 3 to 5 minutes. Using 2 skewers, flip the pancakes over and cook until golden and crispy, about 3 minutes more. Transfer the pancakes to a plate. Repeat with the remaining batter.
Dust the pancakes with confectioners sugar and serve warm. Makes about 40.