The golden caramelized top gives this cake its distinctive look and taste.
Preheat oven to 350 degrees. In a large bowl, combine flour, baking powder, and salt; set aside.
With an electric mixer, cream 6 tablespoons butter and 1 cup sugar until light and fluffy. Add eggs and vanilla; beat until combined. Add flour mixture in 3 additions alternately with the milk in 2, beginning and ending with the flour. Mix just until combined
In a 10-inch cast-iron (or ovenproof nonstick) skillet over low, add remaining sugar and butter and cook, stirring, until the mixture is a light caramel color. Remove from heat and top with pineapple rounds.
Carefully spoon batter over pineapples in skillet. Bake until a toothpick inserted in the center comes out clean, about 45 minutes.
Let cake cool in pan 5 minutes. Run a knife around edge of cake, then carefully invert onto a platter. Serve warm or at room temperature.
You will need about half of a small pineapple for this recipe. When heated, sugar melts and turns an amber color; this is caramelized sugar. Be sure to stir frequently so that it colors evenly.