• Make the In-N-Out spread and refrigerate until ready to use. (recipe is located below this one)

MAKE THE BEEF FILLING:

• In a 10 or 12-inch skillet, add unsalted butter and the diced yellow onion with a pinch of kosher salt. Cook over medium to medium-low heat, stirring often until the onions are tender and caramelized, about 15 to 20 mintues.
• Meanwhile preheat your oven to 375°F (or 190°C).
• To the caramelized onions, add in the ground beef. Use a spatula to break up the meat into small crumbles, tossing with the caramelized onions and fully cooked. Drain and discard any fat from the pan. Measure and add au jus gravy mix. Stir until combined and remove off of the heat.

BUILD THE SLIDERS:

• Line a rimmed baking sheet with parchment paper. Using a serrated bread knife, slice the slider buns in half horizontally, placing the bottom half of the sliders onto the prepared pan. Top with 6 to 8 slices of American cheese and top with the beef and onion mixture and spread it in an even layer. Drizzle with 1/3 cup of the In-N-Out spread, top with 4 to 6 more slices of American cheese, tearing them to fit if necessary.
• Replace the top half of the sliders and bake in your preheated oven for 8 minutes or until the cheese has melted and the sliders are heated through. Serve with French fries or any side of your choice, spicy peppers and extra sauce on the side.