Preheat oven to 350F. Drain the pineapple slices, reserving 2 T syrup. In a heavy cast iron frying pan (10"), melt the butter over medium heat. Add brown sugar, stirring until the sugar is melted. Remove from heat, and arrange 8 of the pineapple slices on the sugar mixture, overlapping the slices slightly around the edge of the pan. Put one slice in the center. Place the walnut or pecan halves in the center of each slice of pineapple. Arrange around the inside edge of the skillet the remaining pineapple, cut in halves. Put pecans or walnuts in the center. In a medium bowl, mix the flour, sugar, baking powder, and salt.Add shortening and milk. Beat 2 minutes at high speed or until mixture is smooth.Add egg and reserved 2 T of syrup. Beat 2 minutes longer. Gently pour cake batter over pineapple in skillet. Spread evenly being careful not to disarrange the pineapple. Place on center rack of oven and bake 40-45 minutes, or until cake springs back to light touch. After the cake is done, let the skillet stand on a wire rack 5 minutes to cool just slightly, and then loosen edges with a small spatula. Place serving platter over the cake, and turn upside down. Shake gently, and lift off skillet. Serve with 1 cup heavy cream whipped.