In a small bowl, cream together the butter, sugar, cinnamon, nutmeg, cloves, and salt. Refrigerate until almost firm. Spoon about 2 tablespoons of the butter mixture into 12 small mugs. If you’re snowed in and your guests can’t make it you can keep the mixture refrigerated. I always like to make a big batch of the mixture to keep on hand, so I’m ready for any drop by guests. Pour about 3 ounces of rum into each mug. Top with boiling water, stir well and serve immediately.