Preheat oven to 325°. Place chopped pecans and 1 tablespoon butter in a baking pan. Bake 5-7 minutes or until pecans are toasted and browned, stirring frequently. Set aside to cool. , In a large bowl, cream brown sugar and remaining butter until light and fluffy, 5-7 minutes. Beat in egg yolk and vanilla. Gradually add flour and mix well. Cover and refrigerate 1 hour or until easy to handle. , Preheat oven to 375°. Roll dough into 1-in. balls, then roll balls in toasted pecans, pressing nuts into dough. Place 2 in. apart on ungreased baking sheets. Beat egg white until foamy. Dip pecan halves into egg white, then gently press 1 into each ball. , Bake at 375° until golden brown, 10-12 minutes. Cool for 2 minutes before removing to wire racks.