Thumbprint cookies filled with jam are a delicious treat all year long.
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.