**Make the Spread:**

1. In a small bowl, mix mayonnaise, relish, ketchup, sugar, and vinegar. Set aside.

**Prepare the Patties:**

1. Weigh out 8 portions of 3 to 4 oz of ground beef. Gently flatten each patty, sprinkle with salt and pepper on both sides, and set aside.

**Caramelize the Onion Buns:**

1. In a pan over medium to medium-low heat, add vegetable oil. Cook onions with sugar and salt until golden. Add cheese to half the grilled onions.

**Cook and Assemble the Burger:**

1. In a skillet over medium-high heat, add vegetable oil and/or butter. Cook patties, optionally spreading mustard on the raw side. Flip, add cheese, and cook for 1 more minute. Create a double double burger by stacking a patty without cheese on top of a patty with cheese. Transfer onto a grilled onion and top with another grilled onion with cheese.
2. Serve with the spread and enjoy your warm, homemade creation!