Step 1
Prep the onions and mushrooms with a knife, or in a food processor. Add to a large sauté pan with the butter and oil, and cook on med-high heat, for about 10 minutes, until the moisture from the mushrooms is evaporated, and the mixture is lightly browned. Add to a large mixing bowl. Allow to cool for 15 minutes.
Step 2
Add all the remaining ingredients, except the meat, and mix well. Add the meat and mix gently until combined. Do not over-mix.
Step 3
Preheat oven to 325 degrees F. - Lightly grease the bottom of a shallow roasting pan with a few drops of oil. Wet your hands with cold water and form the meatloaf mixture into a loaf shape, about 6 inches wide, by about 3 to 4 inches high.