Combine the first 3 ingredients in a bowl; beat at medium speed of a mixer until blended. Add egg and egg white; beat well. Combine flour, cocoa, baking soda, and salt; stir well. Gradually add to molasses mixture, beating well. Stir in 1/2 cup chips, milk, and vanilla.
Drop the dough by level tablespoons onto baking sheets coated with cooking spray. Bake at 325° for 12 minutes; let cool on pans 1 minute. Remove from pans; let cool completely on wire racks.
Place remaining chips in a small zip-top heavy-duty plastic bag, and seal bag. Submerge bag in very hot water until chips melt. Snip a tiny hole in 1 corner of bag, and drizzle chocolate over cookies.