Step 1 — Preheat & season the beef: Preheat your oven to 350°F. In a large bowl, gently combine the ground meat with the Lawry's, garlic powder, and black pepper. And I mean GENTLY — use your fingertips and just work the seasoning through until it's evenly distributed. Overmixing is how you end up with tough, dense sliders, and we're not doing that.
Step 2 — Mustard the pan: Squeeze the yellow mustard all over the bottom of a 9×13 Pyrex baking dish and spread it into an even layer so the whole bottom is covered. I know it looks strange — trust the process! The mustard bakes right into the beef and gives it that tangy, griddled flavor that makes these sliders famous.
Step 3 — Press in the beef & bake: Press the seasoned ground meat evenly into the pan, right over the mustard, all the way to the corners like one big patty. Bake for 15–20 minutes, until the beef is cooked through. No flipping, no forming little patties — the oven does all the work.
Step 4 — Saute the onions: While the beef bakes, heat 1 tablespoon of vegetable oil and 1 tablespoon of butter in a skillet over medium heat. Add the chopped onion with a sprinkle of salt and pepper and cook, stirring occasionally, until soft and translucent, about 8–10 minutes. Sweet, golden onions are half the magic here — don't rush them.
Step 5 — Mix the secret sauce: In a small bowl, stir together the mayo, yellow mustard, and cayenne until smooth. If you doubled it for dipping (smart move), set half aside in a serving bowl now before it disappears.
Step 6 — Remove the beef & reset the pan: When the beef comes out, carefully lift the whole patty out of the dish using two spatulas — one on each end — and set it on a plate or cutting board. Pour off any grease, then wash the baking dish and spray it with Pam. (Shortcut: if you have two 9×13 dishes, just assemble in the clean one.) Step 7 — Slice the rolls: Using a serrated bread knife, slice the entire sheet of King's Hawaiian rolls in half horizontally, keeping the tops and bottoms connected as one piece. This keeps assembly fast and the sliders picture-perfect. Step 8 — Build the sliders: Place the bottom buns in the greased dish. Now layer in this exact order: muenster cheese slices first (this is the sogginess shield — always cheese before meat!), then flip the beef patty on top MUSTARD SIDE UP, then the sauteed onions, then the pickle chips, then the cheddar slices. Spread the secret sauce on the cut side of the top buns, and set the tops on to close everything up. Step 9 — Make the butter pour: Melt the stick of salted butter and stir in the tri-color sesame seeds (or poppy seeds) and a few cracks of black pepper. Pour it slowly and evenly over the tops of the sliders so every roll gets that buttery, seedy glow.
Step 10 — Bake to golden perfection: Bake at 350°F for 15–20 minutes total — covered with aluminum foil for the first half (this melts all the cheese without drying the buns), then uncovered for the last half so the tops turn golden and glossy. Lift the sliders out of the dish with two spatulas as soon as they're done, THEN slice and serve. Watch them vanish!
