Whenever Mr. T and I go out to a steakhouse I get the mushrooms and onion add on. I love them and in my opinion mushrooms and onions are a must have with a steak.
Mushrooms and Onions:
1 sweet onion, sliced
1 carton of mushrooms, baby bellas or button, sliced
1 tablespoon of olive oil
2 tablespoons butter
1 teaspoon steak seasoning
Heat a skillet over high heat. Add the olive oil and butter and let melt together. Add the mushrooms, onion, and steak seasoning. Cook, stirring randomly, until the onions are starting to turn soft and get a little brown on the edges.