Preheat oven to 350°. In a large bowl, cream butter, brown sugar and salt until light and fluffy, 5-7 minutes. Beat in egg yolk, milk and vanilla. Gradually beat flour into creamed mixture. Stir in chocolate chips. Cover and refrigerate 1 hour or until firm enough to shape.
Shape tablespoons of dough into balls. Dip balls into egg white; roll in pecans. Place 2 in. apart on lightly greased baking sheets. Press a deep indentation in center of each with your thumb. Bake until light golden brown, 12-14 minutes.
Remove from pans to wire racks to cool completely. Fill each with 1 teaspoon cookie spread. If desired, sprinkle with additional chocolate chips.