Add the butter and oil to a large skillet and let melt over medium-high heat. (See notes if using a pan in which you already pan-seared some meat).
Add the mushrooms and spread out over the pan. Let cook, undisturbed, for 2 minutes to brown. Then stir and cook until tender, another 2 to 3 minutes.
Stir in the garlic and rosemary and cook 1 minutes more, until fragrant. Sprinkle with the salt and pepper. Add the wine to deglaze the pan, scraping up any browned bits. Cook until most of the liquid has evaporated.
Stir in the broth and bring to a boil. Cook 2 minutes, then push the mushrooms to one side of the pan. Sprinkle the liquid with the glucomannan and whisk well. Stir everything together and let cool a few minutes before serving.
Remove from heat and stir everything together. Let cool a few minutes before serving.
If you plan on cooking some pork chops or other meat in a pan, you can make the gravy in the same pan and use the pan juices and oils. This is actually my favorite way to make the mushroom gravy, as it adds flavor.
Simply remove the meat to a platter and tent with foil to stay warm.
Add the butter to the pan, as in Step 1. You may not need to add more oil at all, depending on what was left over from cooking the meat. Aim for about 4 tablespoons of butter and oil in the pan before adding the mushrooms.