In a medium bowl, stir together the peanut butter, sugar, egg, and vanilla extract until thoroughly combined. Using your hands, roll the dough into 1 inch balls and place them about 2 inches apart on a parchment lined baking sheet. Lightly press a small, shallow indentation in top of each ball using your thumb. Fill the center of each cookie with the fruit preserves. If the fruit preserves are too thick, vigorously stir it in a small bowl until the consistency thins out and is easier to work with.
Bake for 8 to 11 minutes or until lightly browned. Do not overbake. The cookies will become firmer as they cool. Allow the cookies to cool on the baking sheet for 5 minutes or until set before transferring to a wire rack to cool completely.