Why does breakfast casserole need to be refrigerated overnight?

Breakfast casserole doesn't *need* to be refrigerated overnight, but it's highly recommended for two main reasons:

1. Flavor Development: Many breakfast casseroles include ingredients like cheese, eggs, and milk, which benefit from time to meld together and develop deeper flavors. Letting the casserole sit in the fridge overnight allows these ingredients to marry and creates a richer, more flavorful dish.

2. Better Texture: The overnight chill helps the casserole set and solidify, resulting in a sliceable, firm texture rather than a soggy mess. This is especially important for casseroles with a lot of vegetables, which can become mushy if not chilled properly.

However, there are some exceptions:

* Pre-made casseroles: If you're buying a pre-made breakfast casserole from the grocery store, it usually doesn't need to be refrigerated overnight. The manufacturer has already accounted for the proper chilling and setting time during production.

* Casseroles without dairy: Some breakfast casseroles might be made with ingredients like bread, vegetables, and sausage, which might not benefit significantly from overnight chilling.

Ultimately, the decision of whether or not to refrigerate your breakfast casserole overnight comes down to your personal preference and the specific ingredients you're using. If you have the time, it's generally a good idea to let it chill for a more flavorful and well-textured result.