Coconut Shortbreads

• 8 ounces cold unsalted butter, cut into ¼-inch bits, plus additional for the tart pans
• 2 cups all-purpose flour

Preheat the oven to 350°F. Lightly butter two 9-inch tart pans with removable bottoms. Using an electric mixer fitted with the paddle attachment, or by hand with a wooden spoon in a large bowl, combine the butter, flour, sugar, salt, coconut, egg yolk, lemon zest, lemon juice, and vani