Charming thumbprint jam cookies with a buttery base and jewel-toned preserves are a beautiful family holiday tradition. These elegant little cookies add color and sweetness to any cookie platter.
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream the unsalted butter and granulated sugar together using a mixer on medium speed until light and fluffy, about 2–3 minutes.
Add the egg yolk and vanilla extract; beat until well combined, scraping down the sides as needed.
Gradually mix in all-purpose flour and salt on low speed until a soft dough forms; do not overmix.
Roll dough into 1-inch balls, place on prepared baking sheet, and press each center lightly with your thumb to make an indentation.
Fill each indentation with about 1/2 tsp fruit preserves, being careful not to overfill.
Bake for 12–15 minutes, rotating the tray halfway through, until edges are pale golden.
Cool cookies on the sheet for 3 minutes, then transfer to a wire rack to cool completely for optimal texture.