Preheat oven to 350°F (175°C) and line two baking sheets with parchment.

Beat the butter and powdered sugar until light and fluffy, about 2 minutes.

Mix in the vanilla and salt, then gradually add the flour, stirring just until combined.

Roll tablespoon-sized dough balls, coat in nuts if using, and place 2 inches apart on the sheets. Press a deep indent into each one and fill with about 1/2 teaspoon of jam.

Bake one sheet at a time for 12 to 14 minutes, until the edges are lightly golden.

Let the cookies cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.