Slice onions and mushrooms and remove the leaves from thyme stems.
In a frying pan on medium high heat add about 1 TB oil and then toss in mushrooms. Cook and stir the mushrooms for about 3 minutes to allow them to release some water.
Then, add in sliced onions. Continue mixing around for about 3-4 minutes. Once the onions and mushrooms start to stick to the bottom of the pan lower the heat to medium.
If the pan gets too dry add a little oil when needed. Continue to stir, let it stick for a second then stir again. This speeds the process up. If you let the mushrooms or onions stick for too long they will burn. You will have to stay at the stove while cooking this recipe.
When the majority is browned and withered lower the heat and to medium low and toss in thyme. Mix it around then toss in butter. Mix well then salt and pepper to taste.
Serve.