How to Make It
Preheat a grill pan over high heat. Grill all of the pineapple wheels until they are charred, about 5 minutes per side. Cut each unpeeled pineapple wheel into 4 wedges and reserve them for garnish.
Cut the peeled pineapple wheels into small pieces. In a blender, puree the peeled pieces, adding up to 1/4 cup pineapple juice to help blend. Strain the puree into a measuring cup, transfer 8 ounces of the grilled pineapple juice to a pitcher (reserve the rest for another use), then stir in the whisky, Scotch, rum, Curaçao, orange juice, lemon juice and grenadine.
Pour half of the mixture into the blender, add 2 cups of ice and blend until slushy. Pour into 8 chilled tiki mugs or hollowed pineapples. Garnish each drink with a grilled pineapple wedge and a cocktail umbrella. Repeat for the remaining servings.