Preheat oven to 350°. In a saucepan, combine brown sugar, butter and milk. Cook and stir over medium heat 3-4 minutes or until slightly thickened. Stir in pecans, flour and vanilla. Drop by 1/2 teaspoonfuls 3 in. apart onto foil-lined baking sheets. Bake 5-7 minutes or until golden brown and lacy. Cool completely before carefully removing from foil., In a microwave, melt chocolate chips; stir until smooth. Spread 1 teaspoon melted chocolate on bottoms of half the cookies; cover with remaining cookies. Refrigerate 10 minutes or until set. Store between pieces of waxed paper in an airtight container.