Wild mushrooms are a pleasure to cook as they are delicate and lend newness to a mushroom dish. Sometimes I add in Button or Cremini mushrooms as well as Shiitake mushrooms although Shiitake lend a significantly distinct flavor.
Here, simply sauté sliced mushrooms in butter and S&P. Add diced onion and soften. Add diced tomato and heat through. I season as I go and adjust at the end. I find it gives my food the best flavor and the most control over the result. Add a tablespoon or so of tomato paste and stir. Add cream and slowly bring to a very gentle almost simmer and reduce until it clings to a wooden spoon. This is lovely smooth and satisfying sauce tossed with any pasta or served on a keto veggie. A fresh herb at the end adds bit of brightness. Enjoy.