Cheesy Skillet French Onion Meatball Sub with Melted Gruyère Step-by-step instructions

Before you start

Before you start, make sure you have all the ingredients ready: sliced onions, minced garlic, softened butter, and shredded cheeses. If using raw meatballs, have them thawed and ready to cook.

Preheat the broiler and position the rack in the upper third of the oven. Have a baking sheet ready for the baguette. This recipe moves quickly once the onions are caramelizing, so prep everything beforehand.

Instructions

Caramelize and Sear

1. 1Caramelize the Onions
   Melt 2 tablespoons of the butter in a large cast-iron skillet over medium heat. Add the sliced onions and cook, stirring occasionally, for 20–25 minutes until deeply caramelized, dark brown, and jammy. Stir in the Worcestershire sauce and beef broth, scraping up any browned bits. Continue cooking for 2–3 minutes until the liquid reduces to a glossy glaze. Transfer the onions to a bowl and set aside.
   Look for Onions are soft, dark brown, and jammy with a sweet, savory aroma.
   Tip Don't rush the onions—low and slow is key to deep caramelization.
2. 2Sear the Meatballs
   Wipe the skillet clean and add the remaining 2 tablespoons of butter. Heat over medium-high heat until shimmering. Add the meatballs in a single layer and sear for 2–3 minutes per side, turning occasionally, until browned all over. Pour the caramelized onions back into the skillet with the meatballs and toss to coat the meatballs in the onion glaze. Cook for 5–7 minutes, stirring, until the meatballs are heated through and the internal temperature reaches 160°F (71°C).
   Look for Meatballs are browned and glossy with onion glaze; they register 160°F (71°C) on an instant-read thermometer.
   Safe temperature 160°F (71°C) internal temperature (ground meat)
   Tip If using raw meatballs, cook them fully in the skillet before adding the onions.

The onions should be soft, dark brown, and jammy with a sweet, savory aroma. The meatballs are browned on all sides and coated in the glossy onion glaze.

The skillet should have a rich, beefy scent. Before moving on, ensure the meatballs are cooked through to 160°F (71°C) if using raw.

Toast and Assemble

3. 3Toast the Baguette
   Preheat the broiler to high. Split the baguette lengthwise and place cut-side up on a baking sheet. Mix the minced garlic with the remaining softened butter (if you used all the butter, soften an extra tablespoon) and spread the garlic butter over the cut sides of the baguette. Broil for 1–2 minutes until golden and toasted.
   Look for Baguette is golden, crisp at the edges, and smells garlicky.
   Tip Watch closely—broilers vary and can burn bread quickly.
4. 4Assemble the Subs
   Spoon the meatball-onion mixture evenly along the bottom half of the toasted baguette. Pile high with the caramelized onions. Sprinkle the shredded Gruyère and provolone evenly over the top, covering the meatballs completely.
   Look for The sub is loaded with meatballs, onions, and a generous layer of cheese.
   Tip Press the cheese gently so it stays on the sub during broiling.

The baguette halves are golden and crisp, with a strong garlic-butter aroma. The sub is assembled with the meatball-onion mixture piled high and the cheese evenly distributed. The cheese should completely cover the meatballs, leaving no bare spots.

Broil and Serve

5. 5Broil Until Bubbly
   Place the assembled sub back under the broiler. Broil for 3–5 minutes, until the cheese is molten, blistered, and golden brown in spots. Keep a close eye to avoid burning.
   Look for Cheese is bubbly, blistered, and golden; the edges are slightly charred.
   Tip Broil on the middle rack to allow the cheese to melt without burning.
6. 6Pull and Serve
   Remove the sub from the broiler and let it rest for 2 minutes. Use a sharp knife to slice the sub into individual portions, pulling apart to reveal the cheese stretch. Serve hot.
   Look for Cheese stretches in long strands as the sub is pulled apart.
   Tip Letting it rest helps the cheese set slightly so it doesn't slide off.

The cheese is molten, bubbly, and blistered with golden-brown spots. The edges of the bread are slightly charred, and the sub is steaming. When pulled apart, the cheese stretches in long, gooey strands. Let it rest for 2 minutes before slicing to allow the cheese to set slightly.

Common mistakes

One common mistake is rushing the onions—cooking them over high heat will burn them before they caramelize. Keep the heat medium-low and stir occasionally.

Another issue is overloading the sub with too much cheese, which can make it hard to eat; a generous but even layer works best. Also, don't skip toasting the baguette, as it provides the crunchy base that holds up to the juicy filling.

How to tell it’s done

The meatballs are done when they are heated through and an instant-read thermometer inserted into the center reads 160°F (71°C). The cheese is done when it is fully melted, bubbly, and golden brown in spots, with a few blistered areas.

The bread should be toasted and crisp around the edges but still soft in the center. Pull the sub apart to check that the cheese stretches and the meatballs are coated in the onion glaze.

• Ground meat: 160°F (71°C) in the thickest part