Preheat oven to 450°F (230°C).

Roll out pastry on a lightly floured surface to 1/8-inch (3 mm) thickness.

Cut out 12 circles using a 4-inch (10 cm) round cookie cutter.

Fit the pastry circles into 2-3/4- x 1-1/4-inch (7 x 3 cm) muffin cups.

Divide currants, raisins, nuts, or coconut among the pastry shells.

In a separate bowl, combine brown sugar, corn syrup, egg, softened butter, vanilla, vinegar, and salt.

Spoon the filling into the pastry shells, filling them three-quarters full.

Bake in the bottom third of the preheated oven for about 12 minutes, or until the filling is puffed, bubbly, and the pastry is golden brown.

Let the tarts stand on a rack for 1 minute.

Run a metal spatula around the tarts to loosen them.

Carefully slide the spatula under the tarts and transfer them to a rack to cool completely.