Clean the mushrooms with a paper towel. The just need a gentle wipe. Cut into quite thick slices
Add butter and oil to a pan and heat over medium high and allow it to get hot. Add the mushrooms to the pan being careful not to crowd the pan, and walk away for about 4 minutes. (well okay...peek a bit to make sure they don't burn, but don't disturb them or stir them.)
Turn the mushrooms and cook another 4 minutes undisturbed.
Stir in the crushed garlic and cook until it is fragrant but be careful not to burn. Garlic can burn very easily. Cook for a couple of minutes.
Add the soy sauce, balsamic vinegar, and brown sugar, stir a bit, and continue cooking. Now you can stir occasionally, or just shake the pan from time to time to coat.
