Add the jam mixture just before serving to keep the meringues light and crisp.
Preheat oven to 225°.
Cover 2 large baking sheets with parchment paper, and secure paper with masking tape.
Place egg whites and cream of tartar in a medium bowl; beat with a mixer at medium speed until soft peaks form. Increase speed to high, and gradually add granulated sugar and then powdered sugar, 1 tablespoon at a time, beating until stiff peaks form. Add vanilla; beat just until combined.
Spoon batter into a large zip-top plastic bag. Seal bag; carefully snip off 1 bottom corner of bag. Pipe 24 mounds onto prepared baking sheets. Moisten thumb or a spoon with water, and press thumb or spoon into center of each mound to form an indentation.
Bake at 225° for 1 1/2 hours. Turn oven off; cool meringues in closed oven 2 hours or until dry. Carefully remove the meringues from paper.
Combine jam and liqueur, stirring with a whisk. Place mixture in a small zip-top plastic bag. Seal bag; carefully snip off 1 bottom corner of bag. Pipe about 1/2 teaspoon jam into indention in each cookie. Serve immediately.