Dice two white onions. In a skillet preheated to medium heat (350 degrees F), add 2-3 tablespoons of neutral oil (like avocado oil), the diced onions, and 2/3 stick of unsalted butter. Stir until butter is melted.
Season with a tablespoon of kosher salt and stir every 5 minutes until onions turn into a paste, about 45 minutes.
Remove excess oil/fat with a paper towel, increase heat to 400 degrees, and stir continuously until onions turn golden brown.
Take 2 jalapeños and slice them into small rings. In a separate skillet with a bit of oil on medium heat, sauté the jalapeños until softened and slightly charred. Set aside.
Prepare the spicy burger spread by mixing 1/2 cup mayo, 1 tablespoon each of ketchup and mustard, 1 tablespoon sweet relish, 1 chopped chipotle pepper, 2 teaspoons each of adobo and white wine vinegar, and 2 teaspoons kosher salt in a bowl. Refrigerate.
Form 1/4 pound patties from 2 pounds of 80/20 ground Chuck, shape to fit Texas toast buns, season with your favorite beef rub, and refrigerate on parchment paper for 15-20 minutes.
Heat a griddle to 375 degrees F and cook about 1/2 pound of bacon. Keep warm in aluminum foil.
Grill the refrigerated patties on the griddle for 4 minutes, season with beef rub, squeeze mustard on top, flip, and grill for another 3 minutes. Add 2 slices of 3 pepper Colby jack cheese to each patty to melt.
Spread the spicy burger mixture on Texas toast buns and toast on the griddle for about 60 seconds per side.
To assemble: Lay down a slice of Texas toast, spread with the spicy burger mixture, add sautéed jalapeño rings, place two beef patties, top with caramelized onions, and cap with another slice of Texas toast.
