Thumbprint cookies are buttery shortbread-style rounds pressed with a thumb before baking and filled with jam once they come out of the oven. They're straightforward to make and ready in about 30 minutes, with no chilling required. Any flavor of jam works, so they're easy to adapt to what you have on hand.
Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
In a large mixing bowl, cream together the softened butter and granulated sugar using an electric mixer on medium speed until the mixture becomes light and fluffy. This should take about 2-3 minutes.
Add the vanilla extract and egg yolk to the creamed mixture, blending until fully incorporated.
Gradually fold in the sifted all-purpose flour and salt into the butter mixture, mixing just until a soft dough forms.
Roll dough into 1-inch balls and place them onto the prepared baking sheet, spacing them about 2 inches apart.
Use your thumb or the back of a spoon to make an indentation in the center of each cookie dough ball.
Fill each indentation with about 1/2 teaspoon of your chosen fruit jam.
Bake the cookies in the preheated oven for 12-15 minutes or until the edges are lightly golden. Let them cool on a wire rack before serving.
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Notes
For a nutty twist, roll the dough balls in finely chopped nuts before making the thumbprint.
To ensure the best texture, make sure the butter is softened to room temperature before mixing.