Preheat oven to 350º

Whisk flour, cornstarch, and salt together; set aside

In another bowl, cream together butter and sugar; add vanilla

Add flour mixture in two batches and continue beating at low speed

Once dough comes together, shape dough into 1-inch balls and place on parchment lined baking sheet

Using a teaspoon or your thumb, make an indent in each dough ball deep enough to hold filling

Refrigerate for about an hour

Once chilled, fill each indent with jam (if you use lemon curd, chocolate, or caramel then fill the cookies after they are baked and cool)

Bake for 13 minutes or until edges are lightly browned

Combine powdered sugar and milk to make the glaze. Drizzle the glaze on cookies