• Preheat the oven to 400 degrees Fahrenheit.

Crust

• In a medium bowl, stir 1 ¼ cup flour and ¼ teaspoon salt together. Use a pastry cutter to cut in ⅓ cup shortening until it is pea-sized.
• Add 4 to 5 tablespoons ice water, one tablespoon at a time, tossing with a fork. Add water and mix until all the flour is moistened and it comes together in a shaggy dough. Use your hands to knead the dough just until it comes together into a ball. Be careful not to over-knead it. This will lead to a tough dough.
• Roll the dough out on a lightly floured surface, turning and flouring the dough as needed until the dough is about ¼ inch thick.
• Use a 3-inch circle cutter to cut out 12 circles of dough. If necessary, gently press the scraps of dough together and let it rest for 5 minutes before rolling out again to cut out additional circles.
• Press the circles of dough into a lightly greased muffin tin so each muffin well looks like an individual tart shell. Set in the fridge while you prepare the filling.

Filling

• Add ¼ cup unsalted butter to a large measuring cup and heat in the microwave for 15-20 seconds or until fully melted.
• Whisk in ¼ cup dark brown sugar, ½ cup light corn syrup, 1 large egg, and ¾ teaspoon vanilla extract. Pour the filling evenly into the chilled dough.
• Bake for 15-18 minutes or until the filling is set. Let cool completely before serving.