8 tablespoons (1 stick) butter, softened
1/3 cup firmly packed light brown sugar
1/4 cup creamy peanut butter
1 large egg yolk
1 teaspoon pure vanilla extract
1 1/2 cups all-purpose flour
1/4 teaspoon salt
1 cup unsalted roasted peanuts, finely chopped
2/3 cup strawberry preserves or jam
1. Preheat oven to 375 degrees F. Using an electric mixer, cream the butter and sugar in a medium bowl. Beat in the peanut butter, egg yolk and vanilla. Stir in the flour and salt. �old in peanuts
2. Form the dough into 1-inch balls. Place 2 inches apart on a greased cookie sheet. Bake for 5 minutes. Using a small melon baller or your thumb (but be careful not to burn yourself), make a deep indentation in the center of each cookie so that it will flatten slightly. With the melon baller, spoon about 1 teaspoon of the preserves into each cookie; do not overfill.
3. Bake for about 15 minutes longer, until the cookies are golden and cracked. Transfer to a rack to cool completely.
These cookies can be stored at room temperature for up to three days in an airtight container.