Why do you put milk in meatloaf?

The reason milk is added in meatloaf is that it soaks the bread crumbs which add needed moisture to the meatloaf. If you personally do not want to use milk you can try using low sodium beef stock, chicken stock, water, or a non-dairy milk substitute.

Should you cook onions before putting in meatloaf?

A wide array of vegetables can be used, including onions, carrots, celery, green peppers, red peppers, and summer squash. One tip is to sauté them in butter or olive oil before adding them to the meatloaf. This will ensure they release more of their moisture into the meatloaf.