Make the cookie dough. Sift flour and baking powder into a large bowl. Add ground pistachios and salt and whisk to blend evenly.

Combine eggs, sugar and lemon zest in a large bowl and beat with an electric hand mixer for about 3 minutes until pale and thick. The mixture should nearly triple in volume. Add lemon juice, vanilla and almond extracts and mix to combine. Add the melted butter and mix to combine.

Add flour mixture to the egg mixture a little at a time and mix on low speed until a soft dough forms, then switch to a spatula and continue gently mixing by hand until evenly combined without over-mixing the dough. The dough will be quite soft. Cover the bowl and refrigerate for 1-2 hours until the dough firms up and becomes stiff.

Preheat oven to 350°F. Line two large cookie sheets with parchment paper.

Use a 1 oz cookie scoop to portion dough and use floured hands to roll into balls. The dough will be sticky. Place dough balls onto prepared baking sheets spacing them 2 inches apart and bake for 13-15 minutes until golden on the bottom and lightly golden around the edges.

Make the glaze. Combine icing sugar with lemon juice and milk in a small bowl and whisk until smooth. You should have a thick, white opaque glaze that flows but is not too runny. Add another teaspoon of lemon juice if needed. Dip each cookie in the glaze, or spoon it over top. Sprinkle on your choice of sprinkles before the icing sets, then let the icing set and dry completely before storing.