01 - Preheat oven to 350°F (175°C). In a mixing bowl, cream together butter, powdered sugar, lemon zest, and lemon extract until light and fluffy. Gradually incorporate all-purpose flour and cornstarch until a soft dough forms.
02 - Roll dough into 1-inch balls and arrange on a baking sheet. Using your thumb or the back of a spoon, create a small indentation in the center of each ball. Bake for 8 to 10 minutes until edges are set but not browned.
03 - Allow cookies to cool on the baking sheet for several minutes, then transfer to a cooling rack. Spoon lemon curd into the center of each blossom once slightly cooled.