Combine flour, salt and sugar together in a food processor, pulsing to mix.
Add cold butter cubes and pulse about 10 times, until it resembles coarse meal with pea-sized pieces of butter. Add ice water 1 T at a time, pulsing once after each tablespoon. Add water just until the crumbly dough holds when pinched together.
Empty dough onto a clean surface and knead a few times. Divide in half and shape into 2 disks and sprinkle lightly with flour. Wrap in plastic wrap and refrigerate 1 hour- 2 days.
Preheat oven to 450. In bowl, whisk together brown sugar, butter, corn syrup, eggs, salt and vanilla. Set aside.
Remove dough from the fridge and let soften at room temp for 5-10 minutes. Roll out on a lightly floured surface to 1/8” thickness. Cut into 3” circles with a cookie cutter or glass. Grease muffin tins and place a circle of dough into each cup. Press dough up sides as far as possible without tearing to fill the cup.
Fill cups with 2 T filling. Bake for 12 minutes in the lower third of the oven. Filling should be puffed up a little and bubbly. *1* Remove from oven and let stand for 1 minute before removing.
Remove tarts by running a knife around each cup to loosen and carefully lift each tart onto a cooling rack. Let cool completely before serving. Store in an airtight container in the fridge. You can also freeze them for up to 2 months.
After cooking, the tops of some of the filling may appear white. I have no idea why it happens to some and not others, but that is perfectly okay!
Dough can also last in freezer for up to 3 months when wrapped in plastic and placed in a freezer bag.
Coconut: mix in a pinch of coconut into each cup before baking
Chocolate chip: sprinkle about 5 chocolate chips in each tart before baking
Heath: sprinkle crushed Heath bar pieces into each tart before baking
Salted: sprinkle a pinch of coarse sea salt on the top of the cups halfway through baking
Peanut butter: melt 1 1/2 t of peanut butter per tart and mix with filling