In a medium frying pan, cook sausage over medium-high heat, stirring to crumble and brown meat evely, about 8 minutes. Drain off fat and discard; set meat aside.
Butter a 9-by13-inch baking dish. Line bottom snugly with a single layer of bread, cut to fit (edges can overlap slightly). Make another layer of bread to fit on top and set aside.
Sprinkle bread with half the cheese, then pour 1 cup of salsa over cheese, and scatter half the sausage over salsa. Cover with the reserved bread slices; repeat to make top layer.
Beat eggs and milk until blended and pour over casserole, moistening top evenly. Cover with plastic wrap and chill 8 to 36 hours. Bake, uncovered, in a 350 degree oven until edges of casserole are browned and center is firm when gently touched, about 50 minutes. Cool 15 minutes on rack. Cut into rectangles. 6 to 8 servings. (Sunset Magazine)