For the pie dough:

1. Cube butter and chill in fridge. Measure out a little more water than you need, add some ice, and keep cold.

2. Whisk dry ingredients together in a medium bowl. Cut in butter with fingers, two knives, or a pastry blender until it resembles coarse crumbs (you want some butter chunks still).

3. Make a well in the center. Pour in a few tablespoons of cold water and the vinegar or vodka, if using. Start mixing the water into the dry ingredients with a fork. Continue adding water, about a tablespoon at a time, until dough looks shaggy and is almost - but not quite - coming together.

4. Knead lightly with your hands just until dough comes together.

5. Wrap in plastic and allow to rest in fridge for at least 30 minutes. (Can be made up to 5 days in advance).

For the tartlet cups:

1. Preheat oven to 375 F.

2. Once rested, remove pie dough from plastic and place on a lightly floured surface. Roll out as thinly as possible.

3. Cut out 24 circles using a biscuit cutter or glass about 2 3/4" wide.

4. Place circles over cavities of mini muffin tin, pressing dough in gently and making sure it is flat against the bottom and sides of pan.

5. Cut out 24 squares of parchment paper, 3 1/2 - 4" on each side**. Press a parchment square into each dough cup, again pressing to adhere to the bottom and sides.

6. Fill each lined cup with a scoop of rice or pie weights.

7. Bake until lightly golden brown and almost cooked through, about 12-15 minutes.

8. Remove parchment and rice and prick each cup gently with a fork. Continue to bake until fully baked through and golden, about another 3-5 minutes. 

9. Allow to cool completely before filling.

For the key lime curd:

1. While tartlet cups are baking, make your curd. Place all ingredients except butter in a stainless steel bowl. Fill a small pot with about 2" of water and place over medium heat. Put bowl of curd ingredients on top of this pot, making sure bowl doesn't touch the water.

2. Bring water to a simmer and cook, whisking curd frequently, until thickened. This may take 5-10 minutes (curd will thicken more as it cools).

3. Remove from heat and whisk in butter.

4. Strain through a fine sieve or sifter into a clean bowl. Add zest of one lime and whisk in.

5. Place in refrigerator and allow to cool completely.

To assemble:

1. Remove cooled pastry cups from muffin tin.

2. Fill with key lime curd, using a spoon, small ice cream scoop, or piping bag. 

If desired, add whipped cream:

Place about 1/2 cup of heavy cream and 1 tsp sugar in a mason jar. Screw on lid and shake vigorously until it holds soft peaks. Put whipped cream in a pastry bag and pipe onto tartlets.

For lime sugar:

1. Using a mortar and pestle, grind sugar and lime zest together until sugar turns greens and smells delightfully citrusy, a few minutes.

2. Sprinkle lightly on top of tarts and whipped cream. Or, simply zest a fresh lemon, orange, or lime over tartlets.

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Keep tarts refrigerated until ready to eat. Best served with margaritas.

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