Preheat oven to 350 degree F. Grease a 13x9x2-inch baking pan; set aside. In a large bowl combine flour, the 2 cups sugar, baking powder, soda, nutmeg, and 1/4 teaspoon salt. Using a pastry blender or two knives, cut in butter until mixture resembles coarse crumbs.

In a small bowl combine buttermilk, eggs, and vanilla. Add to flour mixture all at once; stir just until moistened. Fold in mangoes. Spread in prepared pan. Combine the 1/3 cup sugar and cinnamon. Sprinkle evenly over batter. Bake for 40 to 45 minutes or until a wooden pick inserted near center comes out clean; break crust slightly when inserting pick. (Mango pieces will sink to bottom of coffee cake.) Cool slightly. Serve warm with sweetened whipped cream. Makes 12 to 16 servings.

To make sour milk, place 1 tablespoon lemon juice or vinegar in a measuring cup; add enough milk to equal 1 cup liquid. Let stand for 5 minutes.