Step 1
Preheat the oven to 325 degrees F (165 degrees C).
Step 2
Mix butter and powdered sugar together with a rubber spatula until creamy. Add vanilla extract almond extract salt and egg yolk. Mix with the spatula. Add flour and blend until just combined.
Step 3
Use a sorbet scoop to portion dough into 1/2-ounce (1-tablespoon) balls. Roll balls in a plate of white sugar to coat; roll again between your palms. Place several inches apart on a silicone-lined baking sheet. Flatten balls lightly with your fingers.
Step 4
To make shortbread cookies with a little jam poke a well into each cookie using the end of a thick wooden spoon dusted with powdered sugar or using one of your fingers. Fill cookies with fruit jam. Tap baking sheet against the counter to let jam settle.
Step 5
Bake in the preheated oven until tops are barely blonde and bottoms are slightly golden about 15 minutes. Let cool on a wire rack before icing.
Step 6
Meanwhile mix powdered sugar with a little milk until you have a consistency that will hold its shape when piped. Pipe icing on top of cookies in a zigzag pattern. Let sit for 15 minutes before serving.
Step 7
For a more jam-forward cookie press your thumb into the cookies to make large shallow indentations. Spoon in jam. Tap baking sheet against the counter.
Step 8
Bake until not quite golden brown about 15 minutes. Let rest on pan for 5 minutes before transferring a wire rack. Dust with powdered sugar.