Place hot fudge topping on a small microwave-safe plate. Microwave on HIGH until softened. Dip rims of 2 (14-oz.) glasses in fudge topping to coat; sprinkle with chocolate jimmies. Set glasses aside; reserve remaining topping.

Place ice cream and milk in a blender. Cover and blend until smooth. Pour ⅓ cup shake mixture into each prepared glass. Add 3 drops Hy-Vee green food coloring to shake in blender. Cover and blend just until combined. Pour ⅓ cup of the shake over the back of a spoon into each glass. Repeat using an additional 3 drops of green food coloring, blending and pouring remaining shake over the back of a spoon on top of the lighter green layers in each glass.

Top with desired garnishes, such as whipped topping, ice cream sandwiches, crushed mint cookies, and crème de menthe thins candies. If desired, microwave reserved fudge topping on HIGH for 5 seconds; drizzle over milkshakes.