1. Combine sugar, water, vanilla in a 10.5 inch cast iron skillet. Dot with butter. Starting at the edge of the skillet, arrange the apples in concentric circles on the sugar mixture, filling in the center with any remaining apples.

2. Set the skillet over medium-low heat and cook the apples, basting occasionally until the sugar dissolves, apples are tender and syrup becomes golden, 55-60 min. Remove the skillet from heat and let the apple filling cool 5 min.

3. Meanwhile, preheat oven to 425 deg F. On lightly floured surface, roll out dough to a 12-inch circle. Place dough over filling. Carefully tuck the edge of dough along inside of skillet. Transfer the skillet to oven and bake until the crust is golden, 18 - 20 min.

4. Remove skillet, let cool about 10 min. Invert a large platter on top of skillet. Quickly turn upside down to unmold tart. Serve warm or at room temp.