To make your own breadcrumbs, tear firm, fresh bread into pieces and whirl in a food processor or blender until crumbs form.
1. Preheat oven to 350°F. Bring large pot of salted water to a boil. Add cauliflower florets, and boil 5 to 7 minutes, or until just tender. Drain, reserving 1 cup cooking liquid, and set aside.
2. Melt butter in same pot over medium heat. Whisk in flour, and cook 1 minute, stirring constantly. Whisk in milk, garlic, and reserved cooking liquid, and cook 7 to 10 minutes, or until sauce is thickened, whisking constantly. Remove from heat, and stir in cheese, nutritional yeast, cayenne pepper, and egg yolks until cheese is melted. Fold in cauliflower.
3. Coat 13- x 9-inch baking dish with cooking spray. Spread cauliflower mixture in baking dish, and sprinkle with breadcrumbs. Spray breadcrumbs with cooking spray. Bake 30 minutes, or until casserole is hot and bubbly and breadcrumbs are crisp and brown.