BEST Brown Mushroom Gravy (from scratch)

tablespoons butter, bacon grease, lard or beef drippings
1 yellow onion ,finely chopped
1 clove garlic ,minced
16 ounces fresh mushrooms of choice (I used button mushrooms in the photos) ,cleaned and sliced
4 tablespoons unsalted butter
4 tablespoons all-purpose flour
2 cups strong beef broth
1-2 teaspoons balsamic vinegar (according to taste)
1/2 teaspoon sea salt plus more to taste
1/2 teaspoon sugar
1/4 teaspoon dried thyme
1/4 teaspoon freshly ground black pepper
Optional: For a creamy gravy, add a few tablespoons of heavy cream at the end

Melt the butter (or bacon grease, lard or beef drippings – any of these will yield the most flavor) in a pan over medium-high heat and fry the onions until beginning to brown. Add the garlic and cook another minute.
Add the mushrooms and cook 5-7 minutes or until golden and the liquid from the mushrooms has evaporated.
Add the butter and melt. Add the flour, stir to combine and cook for about 2 minutes, stirring continually.
Add the beef broth, vinegar, thyme, sugar, salt and pepper. Whisk continually until the gravy is thickened. Cover and simmer on low, stirring occasionally, for 5-10 minutes. Add salt and pepper to taste. If you prefer the gravy thinner add a little more water (or heavy cream if using)