01 -
Melt butter in a medium skillet over medium-high heat. Add sliced onions and cook, stirring occasionally, until onions are caramelized and golden brown, about 10 minutes. Reduce heat if onions begin to burn. Transfer onions to the bottom of a 5-6 quart slow cooker.
02 -
In a large bowl, combine lean ground beef, beefy onion soup mix, Italian bread crumbs, eggs, milk, and Worcestershire sauce. Dice five slices of Swiss cheese and incorporate them into the mixture. Mix thoroughly with clean hands until fully combined.
03 -
Shape the meat mixture into a loaf form and place it over the caramelized onions in the slow cooker. Pour the condensed French onion soup evenly over the top of the loaf.
04 -
Cover and cook on low setting for 5 to 6 hours or on high for approximately 3 hours, until the internal temperature reaches 165°F (74°C).
05 -
Five minutes before serving, arrange the remaining three slices of Swiss cheese on top of the meatloaf. Replace the slow cooker cover and allow the cheese to melt fully.
06 -
Optionally garnish with chopped parsley. Slice the meatloaf and serve, optionally spooning the cooking juices over each portion.