Preheat oven to 350 degrees. Spray a 13 x 9 baking dish with olive oil.
Bring a pot of water to boil. Cook pasta according to package directions, adding cauliflower in the last 6 minutes of cooking. Reserve 1 cup of cooking liquid and drain.
Melt butter in the same pot. Whisk in flour and cook for 1 to 2 minutes, whisking constantly. Stir in reserved water, milk, and garlic. Cook for 8 minutes, until sauce is thicken, whisking often.
Turn heat to low and stir in cheese, onion powder, salt, pepper and cayenne. Stir until cheese melts. Remove from heat and slowly stir in egg yolks. Toss with pasta and cauliflower.
Transfer to prepared dish and sprinkle with breadcrumbs. Spray breadcrumbs with cooking spray. Bake for 30 minutes.