In a large bowl, whisk dry ingredients together. In a separate bowl, whisk melted butter with eggs until blended, then whisk in buttermilk and milk. Add wet ingredients to dry ingredients, then stir until just blended. Let batter rest 8 to 10 minutes.
Heat a lightly buttered griddle or cast-iron skillet over moderately high heat. Ladle in batter, about ½ cup at a time. Cook 2 to 3 minutes on one side, until bubbles begin to appear on the surface. Flip pancakes and cook 2 minutes longer, or until browned. Repeat with remaining batter. Serve with warm maple syrup and, if desired, Whipped Maple Mascarpone.