Step 1

Set up your grill for indirect heat. If using a charcoal grill, build the coals on one side only. If using a gas grill, heat one side only.

Step 2

For the caramelized onions: Add the butter, onions and a pinch of salt to a medium saute pan. Place the pan on the indirect heat side of the grill and cook, stirring occasionally until the onions are tender and deeply caramelized, about 1 hour. When ready, remove from the grill and set aside.

Step 3

In a mixing bowl, combine the beef and chorizo. Divide the mixture evenly between 8 deli container lids. Flatten the meat into each lid to create an even disk. Pop the 8 meat disks out of the lids. Add the cheese to the center of 4 of the meat disks, then top with the remaining 4 meat disk and seal the edges.

Step 4

Preheat a large cast-iron pan on the direct heat side of the grill. Season both sides of the burgers with salt and drizzle with olive oil. Place the burgers in the pan and immediately smash them with a spatula. Cook the burgers for about 2 minutes per side. Remove the burgers from the grill. Spread the mayo on the burger buns and toast them on the indirect heat side of the grill.

Step 5

To build: To each bun, add some caramelized onions, a burger, the condiments of your choice and cilantro. Serve!