Prepare the Onions:

• Heat butter and olive oil in a skillet over medium heat.
• Add sliced onions and brown sugar. Cook for 10–15 minutes, stirring occasionally, until golden and caramelized.
• For added depth, stir in balsamic vinegar (optional). Set aside.

 Mix the Meatloaf:

• In a large bowl, combine ground beef, French onion soup mix, breadcrumbs, milk, eggs, shredded Swiss cheese, ketchup, Worcestershire sauce, salt, and pepper.
• Mix until just combined, avoiding overmixing to keep the meatloaf tender.

 Shape and Cook:

• Form the meat mixture into a loaf shape.
• Place the meatloaf in your slow cooker and top with half of the caramelized onions.
• Cook on low for 6–7 hours or high for 3–4 hours.

 Add the Cheese:

• In the last 20 minutes of cooking, top the meatloaf with slices of Swiss cheese and the remaining caramelized onions. Cover and let the cheese melt.

 Serve:

• Let the meatloaf rest for 5 minutes before slicing.
• Garnish with fresh chopped parsley and serve alongside mashed potatoes, roasted vegetables, or a crisp green salad.