The best side to go with a steak is mushrooms, no question about it. I know – Italians will serve you spinach and that is very well if you’re in Florence and have queued all day for the Uffizi Gallery. At home – go for mushrooms.
Porcini (or girolles) work best. Fresh porcini sadly are as unattainable for me as stars in the sky, I make do with dried rehydrated ones, but a cheaper, but still flavoursome option is oysters.
This makes almost a sauce – if you want proper sauce, chop them smaller and add more cream. I like to bake them whole though and pile the unctuous, blue cheesy morsels on top of a perfectly cooked steak. Life doesn’t get better than that, I promise.