Chocolate Mint Whoopie  Pies
["1/2 c. sugar", "3 Tbsp. canola oil", "1 egg", "1 c. all-purpose flour", "1/4 c. baking cocoa", "1/2 tsp. baking soda", "1/4 tsp. salt", "4 Tbsp. fat-free milk, divided", "2 Tbsp. butter or stick margarine, softened", "1 1/3 c. confectioners sugar", "1/8 tsp. mint extract", "4 drops green food coloring (optional)"]
["In a bowl, beat sugar and oil until crumbly. Add egg; beat for 1 minute. Combine flour, cocoa, baking soda and salt. Gradually beat into sugar mixture.", "Add 2 tablespoons milk; mix well.", "With lightly floured hands, roll dough into 36 balls."]
["sugar", "canola oil", "egg", "flour", "baking cocoa", "baking soda", "salt", "milk", "butter", "confectioners sugar", "mint", "coloring"]