In a medium bowl, whisk together the flour, sugar, and salt.

Cut in the cold butter until the mixture resembles coarse breadcrumbs.

Use your hands to work the dough and bring it together. The dough shouldn’t be crumbly, as you're going to roll it out. If necessary, add more milk, but don't add too much, as it'll make the baked crusts soft.

Form into a disc and wrap with plastic wrap.

Chill for 1 hour. You can also freeze it for up to 3 months. While it’s chilling, you can make the filling (below).

Grease eighteen 2.6” (6.5 cm) fluted non-stick mini tart pans

Roll out the dough between 2 pieces of parchment paper to about 1/8 inch (3 mm). I used the bottom of a glass (a cookie cutter would give you better, cleaner-cut edges) to make circles that were about 1/4” (6 mm) wider than the widest part of the tart pans, and I still had to trim some away. Do a test to make sure your circles are the right size for your pans. If the dough becomes hard to work with, stick it in the freezer for a few minutes. Then you’ll be able to very easily remove the circle cut-outs. If the circles don’t come off the parchment paper perfectly, it doesn’t really matter since you’ll be pressing them down into the pans and will likely have to trim some off anyway.

Place a circle cut-out over the top of the greased mini tart pan and press it firmly into place. Be sure to press down around the bottom edge to remove any air pockets.

Prick holes over the bottom (not going all the way through the crust, but almost) with a fork. Repeat with the remaining tartlet pans.

Place in the freezer for 20-30 minutes.

Towards the end of the chill time, preheat the oven to 375 °F (190 °C) and place a baking sheet large enough to fit the tartlet pans in the lower third of your oven.

Place the tartlets directly onto the hot baking sheet and bake for 14-17 minutes, rotating the pan halfway through if you notice them browning too quickly in certain areas, until the sides are nicely browned and the bottom has browned.

Remove the baking sheet and tartlets from the oven and place them on a wire rack to cool for about 15-20 minutes before removing the crusts from the pans. To do that, just turn the pan over and let the crust fall into your hand. It’s important to do this while they’re still a bit warm. They came out super easily.

If making ahead of time, you can put the cooled crusts in an airtight container and store them at room temp for up to 3 days.

In a nonreactive bowl, whisk together the lemon juice, eggs, egg yolks, lemon zest, sugar and salt until smooth.

Place the bowl over a pan of simmering water, ensuring it doesn’t touch the water.

Continuously whisk the mixture until it thickens and reaches a temperature of 175 °F (79 °C), and then immediately remove from the heat. Some sites say 160 °F (71 °C), but mine was still much too runny at this point. The first time I made it, I cooked it to 160 °F, added the butter, realized it wasn’t going to get much thicker, put it back on the heat, and thickened it up more. And it was fine (just saying in case you have the same issue).

Whisk in the butter, one tablespoon at a time, until fully incorporated.

Strain the lemon curd through a fine mesh sieve into a clean, nonreactive bowl.

Cover the surface of the curd with plastic wrap, pressing it directly onto the surface to prevent a skin from forming, or simply stir ocassionally as it cools.

Let cool until room temp, about 1 hour. You can place it in the fridge or freezer and stir occasionally if in a hurry. You can also make this 3 days in advance and keep it refrigerated. I had no issue with scooping it straight from the fridge into the crusts.

I recommend filling the tartlets the day of serving. This is to assure that the crusts are at their very best! They get softer over time.

Preheat the oven to 325 °F (163 °C).

Add 1 tbsp (15 grams) of curd to 18 cooled tartlet shells. Place the filled tartlet shells (out of their pans) directly on a baking sheet.

Place the baking sheet in the oven and bake for 10 minutes. This just helps the curd set.

Let them cool for 10 minutes in their pans on the baking sheet which has been placed on a cooling rack.