Be sure to use sweetened cream of coconut (the type you would use in a piña colada), not coconut milk.
1 can (16 oz.) cream of coconut
1/3 ripe pineapple, peeled and coarsely chopped (about 4 cups)
1 cup evaporated milk
1/2 tsp. vanilla extract
1 cup crushed ice
Combine all ingredients in a blender and blend until smooth.