1 can Guinness Draught (14.9-ounce)
4 tbsp chocolate syrup or chocolate sauce, for drizzling
Semisweet chocolate shavings, for garnish
Place four pint glasses in the freezer to chill. Place the ice cream and Guinness in a blender and blend on high until smooth, about 30 seconds. Drizzle one tablespoon of the chocolate syrup or sauce down the insides of each glass. Divide the shake among the glasses and garnish with chocolate shavings. Serve immediately.