How to Make It
Stir together whiskey, 1 cup water, vermouth, and bitters in a large spouted measuring cup. Pour mixture into a freezer-safe glass bottle or container; secure lid. Freeze at least overnight or up to 1 month. Move to refrigerator 1 hour before serving.
To serve, pour about 1/2 cup whiskey mixture into each of 6 cocktail glasses. Garnish with orange peel twists and maraschino cherries.