Steps

• 1

  When ready to cook, set the Traeger temperature to 375˚F and preheat with the lid closed for 15 minutes.

  375 ˚F / 191 ˚C

• 2

  Place a large cast iron pan on the grill grates and allow it to preheat for 10-15 minutes.

  375 ˚F / 191 ˚C

  00:15

• 3

  In the skillet on the grill, add a teaspoon of olive oil, and 1 1/2 teaspoons of butter to coat the bottom of the pan.

• 4

  Add the onions, season with a pinch of salt and pepper and close lid. Cook for 40 minutes, stirring every 10 minutes, until the onions are a rich brown color.

  375 ˚F / 191 ˚C

  00:40

• 5

  Remove the onions from grill and increase the grill temp to 450˚F. Wipe out the skillet or use a cast iron griddle and place on the grill grates to preheat for 10-15 minutes.

  450 ˚F / 232 ˚C

  00:10

• 6

  For each sandwich, butter 2 slices of bread on one side, that will be touching the pan. Spread a thin layer of mustard and mayo on the other side of the bread slices.

• 7

  Add 2 slices of each fontina, mozzarella, and cheddar cheese, then top with the caramelized onions.

• 8

  Place your sandwiches in the preheated pan or on the griddle and close the lid. Grill for 8-10 minutes per side or until well browned and cheese is completely melted.

  450 ˚F / 232 ˚C

  00:16

• 9

  Remove from grill, slice in half into triangles and serve immediately. Enjoy!