Mix the egg, bread crumbs, parsley, onion powder, garlic powder, salt, pepper, thyme, ground beef, and ground sausage in a large bowl.
Form eight oval patties. Heat the olive oil in a skillet and brown the patties on both sides without cooking them through.
Remove excess grease, melt the butter in the skillet, and cook the sliced onion until tender.
Place the patties in the slow cooker and top with the onion and mushrooms.
Whisk the consommé, wine, Worcestershire sauce, ketchup, and garlic together, then pour the mixture over the patties.
Cook on high for 3 to 4 hours or on low for 6 to 7 hours.
Whisk the cornstarch with the cold water, stir it into the gravy, and cook on high until thickened.
Notes
Recipe facts extracted from the source recipe card; the midpoint of the stated high-heat range is used for the displayed cook time while the full high/low ranges remain in the instructions.