Prepare dough: Cut butter into 1/2 inch cubes. Using fingers or pastry blender, mix all except water until most of the mixture resembles coarse meal and the remainder in small, pea-sied lumps. Drizzle 2T ice water evenly over mixture and gently stir with a fork until incorporated. Test mixture by gently squeezing a small handful. Dough should hold together without crumbling apart. Add more water as necessary, 1T at a time until dough is proper consistency. Turn mixture onto a work surface and divide into 4 equal portions. With heel of hand, smear each portion once in a forward motion to distribute fat. Gather dough together and form it into a disk. Chill, wrapped in plastic, until firm-at least one hour or up to one day ahead.

Peel, halve, and core pears. In a 9 to 10 inch ovenproof skillet or well-seasoned cast iron skillet, heat butter over moderate heat until foam subsides and stir in sugar. (Sugar will not be dissolved). Arrange pears, cut side up, in skillet. Sprinkle pears with cinammon and cook without stirring until sugar mixture forms a deep golden caramel. (10-25 minutes). Cool pears completely in skillet.

Preheat oven to 425. On a lightly floured surface with a floured rolling pin, roll out dough into an 11 inch round (about 1/8 inch thick) and arrange over caramelized pears. Tuck edge in around pears. Bake tart in middle of oven until pastry is golden brown, 30-35 minutes. As soon as tart is done, invert tart onto a plate slightly larger than the skillet.

Serve at room temperature with whipped cream or ice cream.