Heat up a skillet with the butter. Wait for it to melt.
Add in your sliced onions. Fry the onions translucent.
Then add all the sliced portobello mushrooms. Cook them so that they reduce and saute gently.
Season with salt, chopped garlic and black pepper.
Once the mushrooms have reduced in size, pour in the white wine and keep on high to medium heat. Stir cook for 1-2 minutes.
Add the Thyme and let reduce on slow heat until all the liquid is gone.
Serve hot as a side dish with beef steak, roasted chicken, turkey, pork chops, poached salmon or vegetarian meatless meals. See the suggestions in the post.
Video
Notes
You can use dried thyme too or omit it altogether, however fresh thyme really adds value and flavor to the portobello mushrooms.