I just made this, and it turns out quite well.
3/4 cup milk (nonfat to whole, doesn't matter)
1 cup grated cheese
Salt & Pepper to taste
1 TB butter
1 TB white flour (not the whole wheet stuff)
In a microwave safe bowl, melt the butter - usually high for 30 seconds
does it.
Mix in the flour until smooth. Add the milk and microwave on high for
1 minute.
Mix the milk/rue mixture (now that it is hot) until there are no lumps,
then add some salt & pepper. Cover with some plastic wrap and
microwave on high until it just about boils out of the plastic wrap.
Remove the plastic wrap. Add the grated cheese and mix it in. Since
the cheese probably just came out of the fridge, you will need to
microwave it again for a minute to melt the cheese in properly.
Add some hot sauce to make it nacho cheese sauce. Or just put it over
vegetables. It is only one bowl to clean up.