Ruby Red Grapefruit Apple Tarte Tatin

Yield: 8 servings.. Combine flour and salt in an electric mixer. Using a dough hook, gradually mix in 5 ounces butter at low speed. Add about 2 tablespoons water, and mix until dough just holds together. Wrap in plastic and chill one hour, then roll out a circle 9 inches in diameter and 1/8-inch thick. Place between two pieces of plastic wrap, and refrigerate on a small baking sheet. Preheat oven to 375 degrees. Melt remaining butter in a 9-inch cast-iron skillet. Sprinkle sugar over butter, swirl to blend and cook on stove, undisturbed, over moderately high heat until sugar melts and turns deep golden, about 20 minutes. Remove from heat. (Hot caramel can also be made in a nonstick skillet and poured into a deep 9-inch pie pan.) Arrange grapefruit and apple slices in pan: take care, as sugar is hot. Do not worry if caramel hardens before all the fruit is added. Cover fruit with pastry, and neatly tuck edges into pan. Bake 40 minutes, or until pastry is evenly browned. Cool 20 minutes, then carefully invert onto a platter. Serve warm, with whipped cream or ice cream if you like.