In a mixing bowl, whisk together an egg, granulated sugar, cornstarch, a pinch of salt, zest, citrus juice, and vanilla extract until smooth.

In a saucepan, melt butter over medium-low heat, then gently whisk in the mixture. Cook while stirring for about 5-10 minutes until thickened.

Strain through a fine-mesh sieve and chill in the fridge while you prepare the cookie dough.

In a large bowl, cream together softened butter and sugar until light and fluffy, about 3-5 minutes.

Add in the egg and vanilla extract, mixing until fully incorporated.

Grind your choice of freeze-dried fruit into a fine powder, then combine flour and salt in a separate bowl.

Gradually mix the dry ingredients and fruit powder into the wet mixture until a cohesive dough forms.

Scoop the cookie dough into twelve equal portions, rolling into smooth balls. Place on a baking sheet lined with parchment paper.

Create an indentation in the center of each ball using your thumb or a spoon, then refrigerate for at least 30 minutes.

Preheat oven to 350°F (180°C). Bake cookies for about 12 minutes until edges are light golden. Let cool on baking sheet.

Once cooled, fill each indentation with the prepared citrus curd or your favorite jams.