In a medium bowl, whisk together the flour, sugar, and salt.
1 1/4 cups (150 grams) flour, 1/4 cup (50 grams) granulated sugar, 1/2 teaspoon salt
Cut in the cold butter until the mixture takes on the texture of coarse breadcrumbs.
1/2 cup (113 grams) cold unsalted butter
In a separate small bowl, whisk the egg yolks, vanilla, and just 1 1/2 tablespoons of milk (ignore the amount below - it's a technical issue I can't fix). Stir this into the dry ingredients.
1 large egg yolk, 1 teaspoon vanilla extract, 1 1/2 to 2 tablespoons milk
Use your hands to work the dough until it comes together. The dough shouldn't be crumbly, as you'll be rolling it out. If needed, add a bit more milk, but be careful not to overdo it, as too much will result in a softer baked crust.
Shape the dough into a disc and wrap it in plastic wrap.
Refrigerate for 1 hour. You can also freeze it for up to 3 months. While it’s chilling, you can prepare the filling (below).
Grease eighteen 2.6” (6.5 cm) fluted non-stick mini tart pans.
Roll out the dough between two sheets of parchment paper to approximately 1/8 inch (3 mm) thick. I used the bottom of a glass (a cookie cutter would create neater, more uniform edges) to cut out circles about 1/4” (6 mm) wider than the widest part of the tart pans, but I still needed to trim some excess. Do a test to ensure your circles are the right size for your pans. If the dough becomes difficult to handle, pop it in the freezer for a few minutes - this will make peeling off the circle cut-outs much easier. If the circles don’t lift perfectly from the parchment, it’s not an issue since you'll be pressing them into the pans and likely trimming away any extra anyway.
Place a dough circle over a greased mini tart pan and press it firmly into place. Make sure to press down around the bottom edge to eliminate any air pockets.
Prick holes across the bottom (almost all the way through, but not completely) with a fork. Repeat with the remaining tartlet pans.
Freeze for 20-30 minutes.
Towards the end of the chilling time, preheat your oven to 375 °F (190 °C) and place a baking sheet large enough to hold the tartlet pans in the lower third of your oven.
Set the tartlets directly onto the hot baking sheet and bake for 14-17 minutes, rotating the pan halfway through if you notice uneven browning, until the sides are a nice golden brown and the bottoms are well-baked.
Remove the baking sheet and tartlets from the oven and transfer them to a wire rack to cool for 15-20 minutes before taking them out of the pans. To do this, simply flip the pan over and let the crust drop into your hand. It’s best to do this while they’re still slightly warm. They release very easily.
If preparing in advance, store the cooled crusts in an airtight container at room temperature for up to 3 days. You can make the fillings 3 days ahead of time, but I recommend filling and topping the tartlets the day of serving. This is to assure that the crusts are at their best!