Cream the butter, cream cheese, and sugar in a large bowl until light and fluffy

Beat in the egg yolk and vanilla until combined

Gradually mix in the flour and salt until a soft dough forms

Cover and chill the dough in the refrigerator for 30 minutes

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

Roll the dough into 1-inch balls and place 2 inches apart on the prepared sheets

Use your thumb or the back of a spoon to gently press an indentation in the center of each ball

Fill each indentation with about ½ teaspoon of jam

Bake for 12 to 14 minutes or until the edges are just turning golden

Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely