Heat olive oil in saute pan, add butter and melt. Add the mushrooms and let them cook for 3-4 minutes. Add the onion and continue to saute for 5-7 minutes more. Add the cream and parmesan. Let it cook for another few minutes and add frozen peas. You could also add some proscuitto here. Give that a minute or two to warm up. Add the tarragon and finish with salt and pepper.