Chocolate-Filled Sugar Thumbprints

Beat together butter, sugar, salt, egg yolks, and vanilla; beat in flour. Scoop mixture into 2 teaspoon portions and gently roll between your hands to make 1-inch balls; place on parchment-lined baking sheets and use your thumb or the end of a wooden spoon to make an indentation in each one. Roll the edges of each cookie in coarse sugar or white nonpareils. Bake at 350 degrees for 10 minutes, press the center of each cookie with the end of the wooden spoon again, and bake 13 more minutes. Fill cookies with melted chocolate. Nutritional information is based on 1 cookie.