Grate the Swiss cheese.
Mix together the diced onions, shredded Swiss cheese, and mayonnaise. Add salt and lots of cracked black pepper to taste.
Add into a baking dish (I used a 9 x 13).
Bake at 350°F for about 45 minutes or til' browned and bubbly.
Hollow out the bread bowl and add the baked onion dip into the bread bowl. Chop up the extra bread you removed into cubes and use for dipping.
Place the filled bread bowl on a baking sheet lined with foil or parchment paper and top the onion dip with mozzarella (optional) and more cracked black pepper.
Set oven to broil and cook until the top is browned... about 2-3 minutes. Serve and enjoy!
