Preheat your oven to 400°F (200°C).
In a mixing bowl, combine the flour and salt. Add the cold diced butter and use a pastry cutter or your fingers to blend until the mixture resembles coarse crumbs.
Gradually add cold water, one tablespoon at a time, mixing until a dough forms.
Gather the dough into a ball, wrap it in plastic wrap, and refrigerate for about 30 minutes.
In another bowl, whisk together the melted butter, brown sugar, corn syrup, eggs, vanilla extract, and salt until smooth and well combined.
Roll out the chilled pastry dough on a floured surface to a thickness of about ¼ inch. Cut out circles that fit into the muffin tin.
Press each circle into the muffin tin cups to form a pastry shell.
If using, sprinkle a few raisins or nuts into each pastry shell.
Carefully pour the filling into each shell, filling them to just below the edge of the crust.
Bake in the preheated oven for 20-25 minutes, or until the filling is bubbly and the edges are golden.
Remove from the oven and let cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.