Ok, this is singularly one of the most tasty and interesting meals I remember preparing. Actually, eating. Made with a surprising combination of ingredients.
I used a large beef rib steak that was enough for two. Sprinkle meat with a little salt, black pepper and rosemary (IMPORTANT: meat has to be kept out of the fridge for at least half a day, this is critical to have a soft meat after cooking). Leave it seat for half a hour. Meanwhile slice in tiny slices a big red onion and toss it gently, uncovered, in three spoonfuls olive oil, stirring frequently (add a couple spoonfuls water if too dry). When it is cooked, put the onions in muffin cups and shape small cakes that you will turn out in the serving plates.
For the cannellini mash, I used a can of cooked cannellini. Wash out most of the water in the can and heat cannellini in a small pan adding a little water, adjust with salt. When hot enough, mash the beans with an immersion blender, put the purea in the plates and sprinkle with a little pepper and olive oil.
Roast the meat (barbecue or on a roasting pan) for 3-5 minutes per side, depending on how thick the meat is. When cooked, slice the meat and serve with the sides. A robust red wine is a must.