In a medium skillet, over medium high heat add 1 Tablespoon butter and allow it to melt then add 1 yellow onion, sliced. Allow the onions to caramelize while stirring occasionally (about 10 minutes). If they start to burn at all, turn down the heat some.
When done, add the caramelized onions to the bottom of a 5-6 quart slow cooker.
In a large bowl, add 2 pounds lean ground beef, 1 envelope beefy onion soup mix, ¾ cup Italian bread crumbs, 2 large eggs, ¾ cup milk and 1 Tablespoon Worcestershire sauce.
Take 5 slices of Swiss cheese and dice them up into chunks. Add the cheese to the meatloaf mixture in the large bowl.
Mix the meatloaf mixture until combined and shape into a loaf. I find this easiest to do with clean hands.
Careful add the loaf to the slow cooker on top of the caramelized onions.
Next, pour 10.5 ounce can French onion soup over the top of the loaf.
Cover and cook on low for about 5-6 hours or on high for about 3 hours (or until the internal temperature of the meatloaf has reached 165F degrees).
Five minutes before serving, top the meatloaf with the remaining 3 slices of Swiss cheese. Put the cover back on the slow cooker until melted.
Optional: garnish with chopped parsley. Slice and serve. I like to take a little bit of the juices left in the slow cooker and pour it over the slices.