PREHEAT OVEN TO 375F. Cream together granulated sugar and 1/2 cup butter at medium speed in mixer bowl until smooth. Lower speed; add vanilla, nutmeg, eggs, yolks and milk. Mix until incorporated. Add baking powder and salt, then flour and cornmeal. Mix until fluffy. Set aside. Combine remaining 1/4 cup butter, Madeira and pineapple in heavy, 10-inch oven-proof skillet over medium heat and cook 20 minutes. Pineapple will release a lot of liquid. Remove pineapple with slotted spoon and reserve. Continue cooking until liquid is reduced nearly to a glaze. Add brown sugar and cook until mixture becomes smooth, about 2 minutes. Replace pineapple slices, arranging them nicely in syrup. Pour cake batter over fruit. Bake on middle rack 20 to 25 minutes. When done, wooden pick inserted into center of cake will come out clean. Place large platter over skillet and turn upside down to remove cake from skillet. Let cool before serving.