Bring 3 Tbsp lemon juice to a boil in a small saucepan over high heat.

Whisk together 1 whole egg, 1 egg yolk, and 1/3 cup granulated sugar in a medium bowl until smooth.

Slowly drizzle the hot lemon juice into the egg mixture while whisking constantly.

Pour the mixture back into the saucepan and cook over low heat, whisking continuously for 3-4 minutes until it coats the back of a wooden spoon.

Press the curd through a fine sieve into a clean bowl.

Stir in 2 Tbsp cold butter until melted, then cover with plastic wrap touching the surface and refrigerate for at least 8 hours.

Combine 1/4 cup granulated sugar and zest of 1/2 lemon in a food processor and pulse until finely mixed.

Cream 4 oz softened butter, 1 oz powdered sugar, and zest of 1/2 lemon for 2-3 minutes until light and fluffy.

Sift 5 oz flour and a pinch of salt over the butter mixture and mix just until combined.

Preheat oven to 325F and line a baking sheet with parchment paper.

Scoop dough with a tablespoon, roll into balls, coat in lemon sugar, and place 2 inches apart on the sheet.

Press each cookie gently with the back of a tablespoon to create a divot, then freeze for 20 minutes.

Bake for 15-17 minutes, turning the sheet halfway through, until edges are set but not browned.

Press the centers again with a teaspoon to deepen the wells, then cool completely on the sheet.

Fill each cookie with about 1/2 tsp lemon curd and serve immediately.