Prepare a smoker using olive branches. Place the beef tenderloin in the smoker and smoke for 20 minutes.
Preheat the oven to 350 degrees F.
Pat the beef dry and sprinkle with salt and pepper. Heat the butter and oil in a roasting pan over moderately-high heat until the foam subsides. Then brown the beef well on all sides, about 10 minutes. Put the roasting pan with the beef in the middle of the oven and roast until an instant-read thermometer inserted diagonally 2 inches into the center registers 130 degrees F for medium-rare, about 30 minutes.
Transfer to a cutting board and let stand 10 minutes. Then cut into 1/2-inch-thick slices.
To serve, first place the Olive Oil Mashed Potatoes on a plate. Then lean 2 slices beef tenderloin on the potatoes. Place a large spoonful of the Roasted Chili and Olive Ragout around or on top. Garnish with watercress.
Olive Oil Mashed Potatoes:
Peel and quarter the potatoes. Put the potatoes and 1 tablespoon salt in a 3-quart pot and cover with cold water by 1 inch. Bring to a boil, covered with the lid, and then reduce the heat and simmer, partially covered, until the potatoes are very tender, 20 to 25 minutes.
Drain the potatoes in a colander and return to the pot. Add the olive oil and olives, and season with salt and pepper. Mash with a potato masher until smooth.
Roasted Chili and Olive Ragout:
Heat 2 tablespoons olive oil over medium-high heat in a saute pan. Add the red onions and cook, stirring occasionally, until the onions are golden brown, about 6 minutes. Remove from the heat. Add the rest of the olive oil and the olives, parsley and all the roasted peppers. Season with salt and pepper.