Heat the oven to 350°F (175°C) and line baking sheets with parchment paper. Beat the softened butter and granulated sugar for 2–3 minutes, until light and creamy.

Beat in the egg yolks and vanilla extract until smooth. If desired, add 1/4 teaspoon almond extract either alongside the vanilla or in place of a small portion of it.

Add the flour and salt gradually, mixing only until a soft dough forms. Chill the dough for about 30 minutes if it feels soft or sticky.

Shape the dough into approximately 1-inch balls and place them about 2 inches apart on the prepared baking sheets. Roll the balls in finely chopped nuts first if using them.

Press a deep indentation into the center of each ball with your thumb or the rounded end of a small measuring spoon. Fill each hollow with about 1/2 teaspoon of thick jam, taking care not to overfill.

Bake for 10–13 minutes, until the edges are set and only lightly golden while the centers remain fairly pale. Cool the cookies on the baking sheet for 5 minutes, then transfer them to a wire rack.