With the rack in the middle position, preheat the oven to 150 °C (300 °F).
Spread butter on both sides of the tortillas. In a large non-stick skillet, brown tortillas, one at a time, on each side. Place on a baking sheet and sprinkle with cheddar cheese. Place in the oven to melt the cheese while you prepare filling.
In a bowl, combine eggs with milk. Season with salt and pepper.
In the same skillet, brown sausage with onions and pepper in oil over medium heat. Add egg mixture and cook gently, stirring until desired doneness. Season with salt and pepper.
Spoon egg filling into tortillas. Top with tomatoes and roll tightly. Serve with salsa and sour cream.