Thumbprint Cookies With Icing Filling

Directions

1. Set your oven to 325°F. Line a baking sheet with parchment paper or a silicone mat and set aside.
2. In a large bowl, use a hand mixer or stand mixer with paddle attachment to beat the softened butter and 1/3 cup granulated sugar until light and fluffy, about 2–3 minutes.
3. Add the egg yolk, salt, and 1 teaspoon vanilla extract, and mix until combined.
4. Add the flour and mix just until the dough comes together. Avoid overmixing.
5. Using a cookie scoop or spoon, portion out about 1.5 tablespoons of dough per cookie. Roll each portion into a smooth ball between your palms.
6. If you like, roll each ball in additional granulated sugar to coat.
7. Place the dough balls on the prepared baking sheet about 2 inches apart. Use your thumb, finger, or the back of a 1/2 teaspoon to gently press an indent into the center of each ball.
8. If the dough cracks around the edges, gently press the cookie back together with your fingers.
9. Bake for 12–15 minutes, until the cookies are just beginning to turn golden around the edges.
10. Let the cookies cool on the baking sheet for 5–10 minutes, then transfer them to a wire rack to cool completely before filling.
11. In a medium bowl, whisk together the powdered sugar, milk, optional 1/2 teaspoon vanilla extract, and optional gel food coloring until smooth.
12. Transfer the icing to a piping bag or a zip-top bag with a small corner snipped off. Pipe the icing into the cooled cookie indents. Let the icing set slightly before serving.