Perfect Thumbprint Cookies

Step 1
Preheat the oven to 325 degrees F (165 degrees C). Line a baking sheet with a silicone mat.

Step 2
Mix together powdered sugar and butter in a large bowl with a rubber spatula until creamy. Add egg yolk, vanilla, salt, and almond extract; mix well. Blend in flour until just combined.

Step 3
Use a sorbet scoop to portion dough into 1/2-ounce (about 1 tablespoon) balls. Roll each ball in a plate of white sugar to coat; roll again between your palms. Place several inches apart on the prepared baking sheet. Flatten balls lightly with your fingers.

Step 4
For jammier cookies, skip to Step 7. For shortbread-type cookies, poke a well into each ball using a finger or the end of a thick wooden spoon dusted with powdered sugar. Fill wells with fruit jam. Tap the baking sheet against the counter to let jam settle.

Step 5
Bake in the preheated oven until the tops are barely blonde and bottoms are slightly golden, about 15 minutes. Let cool completely on a wire rack before icing.

Step 6
Make icing: Place powdered sugar in a small bowl. Add milk, a little at a time, until icing reaches a consistency that will hold its shape when piped. Pipe over cookies in a zigzag pattern. Let sit for 15 minutes before serving.

Step 7
Press thumb into each ball to make a large, shallow indentation. Spoon in jam. Tap the baking sheet against the counter to let jam settle.

Step 8
Bake in the preheated oven until light golden brown, about 15 minutes. Let cookies rest on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Dust with powdered sugar.