Step 1: Prepare the Dough

• Preheat Oven: Begin by preheating your oven to 350°F (175°C) and lining a baking sheet with parchment paper.
• Cream Butter and Sugar: In a large mixing bowl, cream the softened butter and sugar until the mixture is light and fluffy.
• Add Egg Yolks and Vanilla: Mix in the egg yolks and vanilla extract until well combined.
• Combine with Dry Ingredients: Gradually incorporate the flour and salt, mixing until a soft dough forms.

Step 2: Shape the Cookies

• Form Dough Balls: Take about 1 tablespoon of dough and roll it into a ball.
• Make the Thumbprint: Place the dough balls on the prepared baking sheet, spacing them about 1 inch apart. Press an indentation into the center of each dough ball using your thumb or the back of a small spoon.

Step 3: Fill and Bake

• Add Jam or Leave Plain: Spoon a small amount of jam into the indentation of each cookie. If using icing, leave the thumbprint empty and bake the cookies without filling.
• Bake: Place in the oven and bake for 12-15 minutes, or until the edges turn lightly golden. The jam will set slightly if used.
• Cool: Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

Step 4: Add Icing (If Using)

• Fill with Icing: If the cookies were baked unfilled, prepare icing by mixing powdered sugar with a little milk and food coloring. Fill the thumbprint with the icing once the cookies are cool, allowing it to set.

Variations

• Nutty Flavor: Add finely chopped nuts to the dough or sprinkle them over the jam before baking for added texture and flavor.
• Chocolate Twist: Fill the indentations with a small piece of chocolate instead of jam and bake as usual.