Preheat your Yoder Smokers YS640s Pellet Grill to 450ºF, set up for direct grilling (diffuser door or entire diffuser removed), and with GrillGrate grilling panels installed over the fire box.
Place 8 slices of bacon on a wire jerky rack over a sheet pan. Cook on right side of grill to desired doneness, about 20 minutes.
To make the mushrooms, first place the diced bacon in a 12” cast iron skillet on the GrillGrates over direct heat inside the grill. As the bacon fat begins to render out, add the mushrooms and onions. Cook over medium until softened and browning around the edges. Add the garlic and cook for 30-60 seconds. Stir in the beef base & Worcestershire sauce. Stir to incorporate. Add the half and half. Cook until the half and half is reduced and thickened. Cover with a lid and remove from the grill.
To make the Swiss cheese sauce, place the half and half in a 10” cast iron skillet and bring to a simmer. Stir in the American Swiss cheese first, then Emmental Swiss and finally the Kozlik’s Dijon Classique Mustard. Whisk. Hold warm. Add more half and half as needed to keep creamy.
Smash the burger pucks with a flat grill press while sandwiched in between parchment paper. Press evenly until flattened to your desired size (slightly larger than the diameter of the bun).
Season the top side of the burger patties with Yoder Smokers Beef Rub.
When the bacon on the rack and the mushroom mixture are both finished cooking, increase the grill temperature to 500ºF.
Grill the burgers on the GrillGrates, seasoned side down with the grill door open. Season the tops of the patties with Yoder Smokers Beef Rub before flipping. The burgers are done when nice grill marks are formed and the internal temperature surpasses 155ºF.
Meanwhile, mix the mayonnaise and prepared horseradish. Spread buns with the mixture. Toast buns in a 12” skillet over medium heat until golden brown.
To assemble the burgers, place about one half cup of the mushroom mixture on the toasted bottom bun. Top the mushrooms with the burger patty. Smother the patty with the Swiss cheese sauce. Lay two slices of bacon over the cheese and cover with the toasted top bun.