Cook the pasta as directed on package. Drain and toss with the olive oil to prevent sticking. Set aside.
Generously salt and lightly pepper the steaks. In a large, ovenproof pan, sear the steaks on both sides for about 1 minute per side, then place the pan directly into a 425° oven. Cook about 7 minutes per side for medium rare. To grill instead, cook the steaks over a hot flame for 4 to 5 minutes on each side. After cooking, let the steaks rest for at least 7 minutes, then slice thinly.
In a saucepan, heat the milk over medium-low heat. Melt the butter in a deep skillet over medium heat.
Add the flour to the butter and whisk until the mixture is smooth and turns a very light brown—about 5 minutes. Add the milk, 1 cup at a time, whisking constantly.
When each addition is smooth, add the next. Add the cheeses and continue to whisk until smooth. Add the mushrooms and olives and cook until the mushrooms are done.
Pour the sauce over the cooked pasta and toss to coat evenly. Add the steak and enjoy!