Increase heat (same pan) until it’s very hot but not burning. Add more butter and coarsely chopped mushrooms (about a cup). Toss mushrooms quickly on high heat to sear. Do not over-cook. No seasoning. Add to the onions in the warming dish. Deglaze the pan with your favourite brandy, perhaps Asbach Uralt. Use about a quarter cup. Add liquid to mushrooms and onions dish.
While onions are cooking in a small saucepan, on medium high heat, reduce a half-cup of good, red Balsamic vinegar until it is very thick syrup. (Careful not to burn and careful because it will turn hard like sugar candy, and you don’t want that to happen). Into the small saucepan, add the onion mushroom mixture and a few ounces of cold Cambozola cheese. Take away the rind first. Cover until the cheese is melted. Incorporate with a quick stir.
Serve this mixture over your favourite grilled or barbecued steak, done any way you like it, with or without garlic rub or steak spices.
If there is enough sauce for leftovers, it will keep in a covered container in the fridge for a couple of days, and will taste even better. Double or quadruple ingredients and store ahead of time for a large dinner party.
Since this recipe can be made in less than 15 minutes complete, it is a very easy recipe for entertaining with steak of any kind. Try this sauce with flank steak, thinly sliced or with strip sirloin done medium rare. It is also a great topper for any kind of rice as a side dish.