2 cups vanilla ice cream
1 1/4 cups milk
1/4 teaspoon mint extract, or more to taste
9 drops green food coloring
2 tablespoons chocolate syrup, or to taste (optional)
2 tablespoons whipped cream, or to taste (optional)
1/2 teaspoon green decorator sugar, or to taste (optional)
Blend ice cream, milk, mint extract, and food coloring together in a blender until smooth.
Drizzle chocolate syrup around inside walls of 2 tall glasses; pour shake into glass. Top with whipped cream and green decorator sugar.