Preheat oven to 375°F. Butter 8 cups in a standard muffin tin; set aside. In a food processor, combine flour, 1 tablespoon sugar and salt. Add butter and pulse until mixture resembles coarse meal. Add 2 tablespoons sour cream and 2 1/2 tablespoons ice-cold water and pulse just until mixture starts to come together. On a floured surface, roll out dough into an 8x16 inch rectangle and cut into 8 (4-inch) circles. Line muffin cups with dough, pressing dough up the sides of the cups and pressing together any tears.

In a medium bowl, whisk together 1/3 cup brown sugar, remaining 1/2 cup sour cream and eggs; divide between 8 muffin cups. Arrange fruit in custard (some will stick out). Sprinkle with nutmeg and remaining 1 tablespoon sugar. Bake until pastry is golden brown and fruit is tender, about 45 minutes. Run a knife around the edge of each tart to loosen them; immediately transfer to a wire rack to cool slightly. Serve warm or at room temperature.