Preheat oven to 400 degrees F.

Cream together the butter and brown sugar. Add egg yolk and mix well. Add flour and stir to combine.

In a small bowl, beat the egg white until frothy.

Put chopped nuts in a separate small bowl.

Roll tablespoon-size pieces of dough in egg white, then nuts.

Place on ungreased cookie sheets. Let the kids put their thumbprints in the middle (even two-year-olds love this!). Bake for 5 minutes then reduce heat to 300 degrees F and bake for 15 minutes more.

When cooled, put jam in thumbprint.

*To bake these cookies ahead, freeze without the jam, then add when serving.