Combine flour, sugar, cornmeal, baking powder and salt in a bowl. Cut in butter until the texture is coarse and crumbly. Blend into grated cheddar. Stir together sour cream and water adding half and then half again (if needed) just until dough comes together. Shape into a disc, wrap and chill for at least 30 minutes before rolling.
Preheat oven to 350° F. Mix ricotta cheese with grated cheddar to combine and set aside. Toss sliced apples with sugar and cinnamon to coat and set aside. Roll out dough to 1/8-inch thick on a lightly floured surface. Transfer dough into removable-bottom tart pan and trim edges. Spoon cheese filling evenly over dough. Arrange apples evenly on top of cheese filling. Bake for 35 to 45 minutes, until pastry is a rich golden brown.
Cool tart for 10 minutes, then brush entire surface of tart with maple syrup. Tart is best served warm.
Yield: One 3 1/2 x 13-inch rectangular tart pan. Makes 6 to 8 servings.