Lightly grease a 3-quart (or 9x13 inch) baking dish.
Arrange the uncooked ravioli in a single, even layer.
Sprinkle the chopped sun-dried tomatoes over the ravioli, then top with the shredded cheddar, Monterey Jack, and grated Parmesan cheeses.
In a large bowl, whisk together the eggs, milk, salt, and pepper until smooth and fully combined. Carefully pour this egg mixture evenly over the cheese and ravioli in the baking dish.
Cover tightly with plastic wrap or a lid and refrigerate overnight, or for at least 8 hours.
When ready to bake, preheat your oven to 350°F / 175°C.
Remove the cover from the baking dish and bake for 40-45 minutes, or until the casserole is puffed, golden brown, and a knife inserted into the center comes out clean.
Let the bake stand for 10 minutes before slicing and serving.
Garnish generously with fresh basil or parsley.
Add more veggies by stirring 1 cup (240 ml) of wilted spinach or sautéed mushrooms into the ravioli layer before adding the cheese.
Letting the casserole stand for 10 minutes is crucial. It allows the custard to set completely, making it much easier to slice and serve clean portions.