Prepare the lemon curd a day in advance. In a saucepan, combine fresh lemon juice, sugar, and eggs over medium heat, stirring constantly for 10-12 minutes until thickened. Remove from heat, stir in butter until melted, and chill for at least 4 hours or overnight.

In a mixing bowl, cream together the unsalted butter and granulated sugar until light and fluffy, about 3-4 minutes. Beat in the eggs one at a time, then gradually add all-purpose flour, baking powder, and salt to form a dough.

Shape the cookie dough into a log, wrap in plastic wrap, and freeze for about 10 minutes.

Preheat your oven to 360°F (180°C) and line two baking sheets with parchment paper. Roll out the dough to about ¼ inch thickness, cut out flower shapes, and make centers in half the cookies.

Transfer cookies to baking sheets, spacing them apart. Bake for 10-12 minutes until lightly golden. Remove and let cool.

Dust cooled cookies with icing sugar. Pipe or spoon lemon curd onto half the cookies and sandwich them with the other halves.