Add the macaroni, water, and salt to a microwave-safe bowl (I prefer to use a plastic, BPA-free storage container with handles). Microwave (uncovered) on high for 2 minutes, then stir carefully. While the pasta cooks, watch to be sure that the water doesn't foam over the sides of the bowl: if it does, simply open the microwave, remove the bowl (see Recipe Note #2), and stir carefully. If the pasta dries out during the cook time, add an additional 2 tbsp. of water and stir to loosen.
Continue microwaving and stirring at 2-minute intervals for a total of 6 minutes. Carefully check (IT'S HOT!) to see if the macaroni is soft enough for your taste. If not, continue microwaving for 2-minute intervals, if necessary—up to a total of 10 minutes—until the macaroni is just under al dente. This cooking time will vary considerably depending on the wattage of your microwave.
Stir in the milk, along with the mustard, herbs, and hot sauce or paprika (if using). Microwave for 30 seconds more. Stir the American cheese and cream (if using); microwave for an additional 30 seconds. Stir in the cheddar cheese (it may not all melt right away); cover the bowl, letting it stand for 3 minutes. Stir well, sprinkle with black pepper (if using), and serve immediately.