Cut each onion in half and then slice it into 1/4-inch pieces.
Dust any dirt off the cremini mushrooms and cut the bottom of the stems off. Then, thinly and evenly slice the mushrooms.
Add the olive oil, sliced onions, sliced mushrooms, salt, pepper, and thyme sprigs to a large skillet over low heat on the stove.
Let the mushrooms cook and the onions caramelize on low for at least 45 minutes to an hour, moving them around periodically, about every 5-7 minutes, so they don’t burn.
The onions are caramelized when they are golden brown, and the mushrooms are done when they have shrunk in size. Carefully remove the thyme sprigs from the pan and add the crushed garlic. Cook the garlic in the pan. Then, use your spatula to deglaze the pan and get any brown bits off the bottom.
Add the balsamic glaze to the pan and mix. Let the balsamic glaze cook down for 5-10 minutes over low heat.
Once done, let slightly cool, and top with goat cheese, fresh thyme, and chopped fresh flat-leaf parsley.