Mix the ground beef, breadcrumbs, onion, salt, pepper, nutmeg, milk and egg in a large bowl until well-combined.
Form into 36 (1 1/4-inch) balls. Place on a cookie sheet.
Heat the butter and oil in a large nonstick skillet over medium heat. Add the meatballs, cooking in batches if necessary. Cook until browned on all sides, removing the browned meatballs to make room for additional meatballs.
Return all browned meatballs to the skillet and add 1 cup of the consommé. Cover and cook for 20 minutes or until all of the meatballs are completely cooked.
Remove to a serving bowl. Mix the flour with the remaining consommé. Add to the skillet and cook until bubbly, stirring frequently. Stir in the sour cream. Pour over the meatballs.