Make the Pastry Dough:

1. In a large bowl, whisk together the flour and salt. Cut in the cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
2. In a small bowl, mix the ice water and vinegar. Gradually add this to the flour mixture, stirring just until the dough comes together. Do not overmix.
3. Shape the dough into two discs, wrap them in plastic wrap, and refrigerate for at least 30 minutes.

Prepare the Filling: 4. In a medium bowl, whisk together the melted butter, brown sugar, corn syrup, eggs, vanilla extract, and salt until smooth and well combined. If using raisins or pecans, add them to the filling mixture.

Assemble the Butter Tarts: 5. Preheat your oven to 375°F (190°C). Grease a standard 12-cup muffin tin or line it with pastry shells. 6. On a floured surface, roll out one dough disc to about 1/8-inch thickness. Use a round cutter (about 4 inches in diameter) to cut circles. Press each circle gently into the muffin cups, ensuring the edges are even. 7. Fill each pastry shell about 2/3 full with the prepared filling.

Bake the Tarts: 8. Bake for 20-25 minutes, or until the filling is set but still slightly jiggly in the center, and the pastry is golden brown. 9. Remove from the oven and allow the tarts to cool in the pan for 10 minutes before carefully transferring them to a wire rack to cool completely.

Serve and Enjoy: 10. Butter tarts can be served warm or at room temperature. Store leftovers in an airtight container for up to 3 days or refrigerate for longer storage.