01 -
In a medium skillet over medium-high heat, melt butter. Add sliced onion and cook, stirring occasionally, until onions are golden and caramelized, about 10 minutes. Reduce heat if browning too fast. Transfer onions to the slow cooker base.
02 -
In a large mixing bowl, combine ground beef, beef-flavored onion soup mix, Italian bread crumbs, eggs, milk, and Worcestershire sauce. Dice five slices of Swiss cheese into small chunks and fold into the mixture. Mix thoroughly with hands until just combined.
03 -
Shape the meat mixture into a loaf and place it carefully on top of the caramelized onions in the slow cooker. Pour the condensed French onion soup evenly over the meatloaf.
04 -
Cover and cook on low for approximately 5 to 6 hours or on high for 3 hours, until the internal temperature reaches 165°F (74°C).
05 -
About 5 minutes before serving, top the meatloaf with the remaining three slices of Swiss cheese. Cover the slow cooker again and allow cheese to melt.
06 -
Optionally garnish with chopped parsley. Slice and serve, pouring some of the remaining juices over each portion if desired.