2 tart apples (Granny Smith, Macoun, Jonathan, etc.), cored (do not peel) and thinly sliced; or 2 large Bartlett pears, cored and thinly sliced
Juice of 1 lemon
1 Tbsp all-purpose flour
1 sheet puff pastry, defrosted according to package directions
2 tsp butter, melted
2 Tbsp granulated sugar
Preheat oven to 375°F.
In a mixing bowl, combine the apple slices and lemon juice, and toss gently. Set aside.
Scatter the flour on your counter top, and unroll the puff pastry on the flour. With a rolling pin, lightly roll out the creases in the pastry. If there's a small hole, push the pastry together with your fingers to patch it.
Fit the pastry into an 8-inch round, or square or rectangular, tart pan, preferably one with a removable bottom. Press the pastry into all corners of the pan and up the sides, with the excess hanging over the edge. Run your rolling pin across the top of the tart pan to cut the excess away (discard the trimmings, or use for mini tartlets).
With two forks, prick the bottom of the tart dough all over. Don't be shy; make lots of pricks, as these will keep the dough from rising.
Remove the apple slices from the bowl, and arrange them in the bottom of the tart. Paint the fruit with the melted butter, and sprinkle the sugar evenly over the apples.
Bake at 375F for 30 minutes.
Remove the tart from the oven and let it sit on a wire rack for 10 minutes or longer. Remove the outer ring from the pan (sit the whole thing on a can, and the ring will fall away), and place on a serving plate. Serve in wedges, warm or at room temperature.