Step 1Heat the oven to 350 degrees. Spray muffin tins with spray oil.
Step 2In a large bowl, whisk together the flour, cornmeal, baking powder, baking soda and salt. Set aside.
Step 3In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using an electric mixer, cream together the butter, sugar and zest until light and fluffy, 3 to 5 minutes. Beat in the eggs, one at a time, until fully incorporated. Slowly beat in the lemon juice, oil, maple syrup and vanilla extract until fully combined.
Step 4In a separate bowl, whisk together the ricotta and mascarpone cheeses.
Step 5Slowly beat in one-third of the flour mixture into the muffin batter, then beat in one-half of the cheese mixture. Beat in half of the remaining flour mixture, then the rest of the cheese. Finally, beat in the last of the flour just until incorporated.
Step 6Portion the batter into the prepared muffin tins and bake until the muffins are puffed and golden, and a toothpick inserted in the center comes out clean, 20 to 25 minutes. Remove and cool the muffins in the tins on a rack for 5 to 10 minutes before removing. Cool completely before glazing.
Step 1Whisk together the powdered sugar, lemon juice and cream to form a glaze. Drizzle a generous tablespoon over each of the muffins and serve immediately, or set aside to allow the glaze to set up before serving.