Melt 4 tablespoons of butter in a large skillet over medium heat. Add the mushrooms to the pan and let the mushrooms cook in the pan for 4-5 minutes before seasoning with salt and pepper. Don't overcrowd the pan, work in batches if you need to, they'll shrink as they cook.
6 tablespoon cold butter, 14 ounces mushrooms, ½ teaspoon kosher salt, ½ teaspoon black pepper
Stir in the minced shallots while the mushrooms are cooking, and sauté for about 2-3 minutes. Stir occasionally so the shallots don't burn. Once the shallots are turning golden and the mushrooms are golden brown, it's time to move to the next step.
1 small shallot
Add the garlic and thyme into the pan and cook for 1 minute. The thyme may pop a bit in the fat, that's okay.
4 sprigs thyme leaves , 2 cloves garlic
Whisk in the flour and cook for 2 minutes, whisking constantly to cook out the raw flour.
¼ cup all purpose flour
Splash in a little of the beef broth, then whisk it in. It'll incorporate into the flour and seize up, just keep adding a small amount of broth at a time and whisking until you add enough broth that it smooths out and becomes liquidy. Then whisk in the rest of the broth and let it simmer for about 6 minutes or until the gravy is reduced and thickened to your liking. Once reduced, taste for seasoning!
2 cups low sodium beef broth, kosher salt and black pepper
Lastly, when the gravy is thick, whisk that last 2 tablespoons of cold butter into the gravy until completely melted in and incorporated. Pour the gravy into a gravy boat or bowl and serve hot.
6 tablespoon cold butter