It took me a long time to come around to microwave ovens. I think I was the last person on the planet to get one, after being urged to by my elderly father! Still, I don't cook in it. All I ever use it for is to heat up a plate of leftovers or melt a bit of butter.
1/2 cup (4 fluid ounces/118 milliliters) water, room temperature
1/8 teaspoon salt
Pinch of coarsely ground black pepper
Pinch of cayenne
Pinch of dry mustard
1/2 tablespoon (0.25 ounce/7 grams) unsalted butter
1/4 packed cup (1 ounce/28 grams) shredded cheddar
1/4 packed cup (1 ounce/28 grams) shredded Monterey jack
1/4 cup (2 fluid ounces/59 milliliters) milk
1/2 teaspoon tapioca flour or cornstarch
Note: It is quite good even with just half this amount of cheese if you happen to be limiting your cheese intake. You can use all cheddar, if you like, but I think the addition of Monterey jack makes it creamier. And, at the same time, you can toast a few fresh breadcrumbs on the stovetop for a pretty topping.