1. Preheat oven to 350 F.
2. In a bowl, mix the butter and sugar.
3. In another bowl add egg yolks and lemon juice. Mix well.
4. Add the flour and mix until a dough is formed. 5. Shape the dough into small balls.
6. Arrange them on cookie sheets about 2 inches apart.
7. Using your thumb or teaspoon make a small dent in the center of each ball.
8. Bake for 12 to 15 minutes or until lightly golden.
9. Cool cookies for 5 minutes before removing to wire rack.
10. Once cooled, fill dents with jam and serve.