On a lightly dusted countertop, roll the pastry out to about 1/4" thick or a 12-inch circle-whatever. Transfer it to a parchment-lined baking sheet and preheat the oven to 375°F.
Toss all the fruit in a large bowl with the lemon juice. Stir together the sugar and flour and sprinkle over the fruit, toss to coat, and mound into the middle of the pastry, spreading it out to within an inch or two (preferably two) of the edge.
Fold the edge over wherever it wants to, enclosing the fruit. If you like, brush the edge of the pastry with milk or cream and sprinkle with sugar.
Bake for 40-45 minutes, until the fruit is bubbly and the crust is golden. Let cool to at least lukewarm before you cut into it. Serve warm, with ice cream or whipped cream.