1/2 cup softened butter
1/2 cup packed brown sugar
1 egg yolk
1/2 teaspoon vanilla
1 cup flour
1/2 teaspoon salt
1/4 teaspoon baking powder
1 cup semisweet chocolate chips
1 tablespoon shortening
1/3 cup sweetened condensed milk
1 teaspoon vanilla
In a large mixing bowl, cream butter and brown sugar until light and fluffy. Beat in egg yolk and vanilla. Combine the flour, salt and baking powder; gradually add to creamed mixture and mix well.
Roll out the dough into a 12"X10" rectangle between two sheets of waxed paper; transfer to a baking sheet and refrigerate for 30 minutes.
Melt chocolate chips and shortening in a small bowl in the microwave or a small pan on the stove; stir in the milk and vanilla. Cool for 10 minutes. Remove waxed paper from dough; spread with filling. Tightly roll up jelly-roll style, starting with a long side. Wrap in plastic wrap; refrigerate for 2 hours or until firm.
Unwrap and cut into 1/4-inch slices. Place 2 inches apart on lightly greased baking sheet. Bake at 375 degrees for 6-7 minutes or until set. Remove from oven and leave cookies on cookie sheet for two minutes before transferring to a large sheet of aluminum foil to cool. Store in an airtight container.