Stir together the sugar and vanilla bean seeds in a small bowl. Using your hands, press the butter as evenly as you can into a 10-inch ovenproof skillet and sprinkle the vanilla sugar on top.
Arrange the apple halves standing upright, with the rounded sides facing outward, in a tight concentric circle around the skillet. Repeat until the skillet is completely filled.
Place the skillet over medium heat and cook until a golden brown caramel forms, 20 to 30 minutes. It's ok if the caramel is a little patchy. Remove the skillet from the heat and let cool for a few minutes.
Meanwhile, roll the pie dough 1/8 inch thick on a lightly floured work surface. Roll onto a rolling pin then unroll it over the skillet. Carefully tuck any overhanging dough inside the skillet.
Bake until the apples are bubbling and the crust is golden brown, about 20 minutes. Let cool to room temperature, then carefully flip onto a serving dish. Cut the tarte tatin into wedges and serve with whipped cream.
Yield:Makes 2 crusts.
Combine the flour, sugar, salt and butter in a food processor. Pulse until the chunks of butter are broken down to the size of peas and the flour feels like wet sand.
Add 1/4 cup of the ice water and process until the dough comes together easily. If the dough immediately clumps apart, pulse in 2 more tablespoons of ice water at a time. Remember, you can always add more water but not more flour, so be careful not to add too much water at once.
Divide the dough in half and shape each into a ball. Loosely wrap each ball in plastic wrap and flatten the dough into a disk about 1 inch thick. Refrigerate for at least 30 minutes and up to overnight.