Make the Tartlet Shells:

• Preheat your oven to 350°F (175°C).
• In a food processor, pulse together the flour, powdered sugar, and salt. Add the cold butter and pulse until the mixture resembles coarse crumbs.
• Add the egg yolk and pulse again until the dough begins to come together. Add ice water, one tablespoon at a time, until the dough forms. If the dough is too dry, add a little more water.
• Turn the dough out onto a lightly floured surface, shape it into a disk, and wrap it in plastic wrap. Chill in the fridge for at least 30 minutes.
• Once chilled, roll out the dough on a floured surface to about 1/8 inch thick. Use a round cookie cutter or glass to cut out circles large enough to fit into your tartlet pans.
• Press the dough into the pans and trim the excess. Prick the bottoms of the shells with a fork to prevent them from puffing up during baking.
• Bake the tartlet shells for 10-12 minutes, or until golden brown. Let them cool completely in the pans.

Make the Lemon Curd:

• In a medium saucepan, combine the lemon juice, lemon zest, and sugar. Heat over medium heat until the sugar dissolves and the mixture is warm.
• In a separate bowl, whisk the egg yolks. Slowly pour the warm lemon mixture into the egg yolks, whisking constantly to prevent curdling.
• Return the mixture to the saucepan and cook over low heat, stirring constantly with a wooden spoon, until the mixture thickens and coats the back of the spoon (about 5-7 minutes).
• Remove from heat and stir in the butter, a little at a time, until smooth. Add a pinch of salt and stir to combine.
• Let the lemon curd cool to room temperature before filling the tartlet shells.

Assemble the Tartlets:

• Once the tartlet shells have cooled and the lemon curd has thickened, spoon or pipe the lemon curd into the cooled tartlet shells. Fill them nearly to the top, but not overflowing.
• Garnish each tartlet with fresh berries and a sprig of mint, if desired.

Chill and Serve:

• Refrigerate the tartlets for at least 1 hour to allow the curd to set completely before serving.