In a blender (I love my Blendtec), blend the ice cream, milk, peppermint extract and food coloring until smooth.
Pour shake into a tall glass cup.
Whip the heavy cream with powdered sugar until stiff peaks. Place some sweetened whipped cream in a piping bag fitted with a tip and pipe a swirl on top. Garnish with sugar crystals.
Notes
*To get sugar crystals on the rim of the glass, pour some water into the base of a small plate, and some green sugar crystals on another plate. Dip the rim of the cup in the water, shaking off any excess water drips, and then dip the wet rim into the green sugar crystals. (Do this before filling with shake and whipped cream.)