2 1/2 pounds sirloin tips, uncut
1/2 (750 milliliter) bottle Burgundy wine
2 (14.5 ounce) cans beef broth
4 portobello mushroom caps, sliced
1/4 cup butter
1 clove garlic, chopped
1/2 teaspoon dried thyme
1/4 teaspoon salt, or to taste
1/2 teaspoon ground black pepper, or to taste
1 shallot, finely chopped
2 tablespoons all-purpose flour
Preheat an outdoor grill for medium-high heat. Melt butter in a large skillet over medium-high heat. Sautee the shallot until transparent, then add mushrooms, and cook, covered, until darkened, about 5 minutes. Remove mushrooms from pan, and set aside. Deglaze the pan with one can of beef broth, and burgundy wine. Increase heat, and bring to a boil. Allow the mixture to boil until it has reduced by 1/3.
Grill the sirloin tips to desired doneness. Season with salt and pepper if desired. Remove to a plate, and set aside.
When the sauce is reduced, stir in the other can of beef broth, and garlic. Return to a boil, and continue to cook for another 5 to 10 minutes. Sauce will be thin like au jus. Whisk in flour, and cook until the sauce is the desired thickness. Taste and adjust seasoning if necessary. Stir in the mushrooms. Serve tips with mushroom sauce spooned over.