01 -
Slice onion into thin slices after halving. Heat butter and olive oil in a pan on medium-low heat. Add onions and 1/4 teaspoon salt. Stir frequently for 45 minutes until onions are deep golden brown.
02 -
Follow instructions on the au jus mix to prepare the sauce. Set aside.
03 -
Slice the Hawaiian rolls in half horizontally, keeping the rolls intact to form a sheet of roll tops and a sheet of roll bottoms.
04 -
Cut cheese slices into quarters. Place 2 quarters on each slider base. Fold roast beef slices and place two folds over the cheese. Add caramelized onions evenly and drizzle approximately 1/2 teaspoon of au jus over the onions. Place 2 more cheese quarters on top of the onions, then add the tops of the Hawaiian rolls.
05 -
Brush a thin layer of au jus over the tops of the rolls and sprinkle fresh thyme, if using. Avoid covering the rolls with aluminum foil to prevent sticking.
06 -
Place the assembled sliders on the middle rack in a preheated oven at 350°F (180°C). Bake for 20-25 minutes until cheese is melted and tops of the rolls are golden. Serve with remaining au jus.