Make the tartlets:

1. Cut the butter into the flour using a pastry cutter until the mixture resembles course breadcrumbs.
2. Stir in the sugar and salt, then add the egg and stir with a fork until just combined. Use your hands to work the mixture into a dough. It might seem too dry at first, but as you mix it it will start to come together.
3. Roll the dough out on a floured surface to 1/8-inch thick*.
4. Cut the pastry into rounds with a cookie cutter** and press into mini muffin tins. Freeze for 30 minutes prior to baking to prevent shrinking.
5. Bake at 350° Fahrenheit for 20 minutes or until golden. Set aside to cool.

Make the lemon curd:

1. Heat lemon juice over medium heat until hot but not boiling.
2. Meanwhile, whisk eggs and yolk in a medium bowl. Gradually whisk in the sugar. While whisking, slowly pour hot lemon juice into the eggs. Return to saucepan and cook over medium heat. Stir constantly with a wooden spoon until mixture registers 170° Fahrenheit and coats the back of a spoon.
3. Remove pan from heat and stir in butter. Once melted, stir in cream, vanilla, and salt. If the curd didn’t come together and thicken, simply return to heat and cook a bit longer, stirring constantly, until it thickens.
4. Curd can be stored in an airtight container in the fridge for up to a week, just cover with plastic wrap to prevent it from drying out.

Assemble the lemon tartlets:

1. Spoon the lemon curd into each tartlet shell.
2. Top each tartlet with a berry (optional) and serve.