Preheat oven to 350°. Cream butter and sugar until light and fluffy. Beat in egg, milk and vanilla. In a separate bowl, whisk flour, cocoa, baking soda and salt; gradually beat into creamed mixture. Stir in chocolate and cherries.
Drop by rounded tablespoonfuls 2 in. apart onto baking sheets lightly coated with cooking spray. Bake until firm, 12-14 minutes. Cool for 1 minute before removing to a wire rack.