Preheat oven to 35 degrees F.
Combine flour, butter, brown sugar, egg yolks, vanilla and salt in a large mixing bowl. Beat at low speed, scraping bowl often, until well mixed (2 to 3 minutes).
Shape dough into one inch balls. Beat egg whites in a small mixing bowl with fork until foamy. Dip each ball of dough into the egg white, then roll in finely chopped peanuts. Place 1 inch apart onto light greased cookie sheets. Make an indentation in center of each cookie with thumb or back of teaspoon. Bake for 8 minutes.
Remove cookies from oven; fill centers with your choice of:
Continue baking for 6 to 10 minutes or until lightly browned.