How should you saute in butter?

Sauteing in butter is not really all that different from sauteing in any other oil: it just takes an awareness of the smoke point, and avoiding it. Consider investing in an IR thermometer that can tell you exactly the temperature of the pan (with or without the oil) so you can heat the pan to exactly the right point. For butter, that is about 350°F, which is not all that much lower than other oils - including EVOO, for example.

One suggestion is to do as the French do (who sauté in butter all the time!) and use clarified butter, which removes the solids from the butter. It's easy to do, and significantly raises the smoke point (as those solids start smoking much earlier than the oil does). Clarified butter has a smoke point of 450°F, as high as peanut oil. You don't even have to go to the extreme that the linked recipe does in clarifying; simply spooning out the bits you can easily see will often be sufficient. You can clarify butter and then refrigerate or freeze it, if you want to do it in large batches.

Second, use a pan that retains heat well - a heavier pan. That will allow you to cook at a lower temperature effectively. A thinner pan will have more hot spots, which lead to smoke sooner.

Third, make sure you're cooking the right amount of food in the right order. Don't crowd the pan too much. I've sauteed mushrooms and similar with no problem in butter; steaming shouldn't be an issue if you have the right amount of food in the pan at once. If you overload it, though, you do end up cooking too slowly and unevenly, and steaming or just mushing your food.

Fourth, salt is your friend when it comes to moisture. If you're cooking something very moist, salt it before cooking it (but after chopping it), give it a bit of time (5-10 minutes at least). This will let the salt remove some of the moisture, particularly from the outside. Then, wipe off the excess salt and the excess moisture with a cloth or paper towel before sauteing. (Don't give it a long time as eventually the moisture goes back in, and your food gets too salty.) This works well for me with things like eggplant or zucchini - remove some moisture, then saute - as well as the thicker mushrooms (like portobello or white mushrooms).