Philly Cheesesteak Breadboxes

Ingredients:

• 1 loaf of unsliced ​​white bread (preferably Pullman), about 25cm long.
• 6 tablespoons unsalted butter
• 12 slices provolone cheese
• 3 tbsp. l. rapeseed oil (canola)
• 1 large yellow onion, thinly sliced ​​into half rings (about 2 cups)
• 1 large red bell pepper, halved, seeded and thinly sliced ​​(about 1 cup)
• 1 large green bell pepper, halved, seeded and thinly sliced ​​(about 1 cup)
• 450 g thinly sliced ​​rare roast beef
• 1 cup store-bought cheese sauce

Preparation:

1. Position a rack in the middle of the oven and preheat the oven to 190°C (375°F). Trim the tops of the bread to a thickness of 0.5 cm, then cut the loaf crosswise into 4 equal pieces. Using a fork, carefully poke a square hole in each piece of bread to create a 1 cm-thick box. Set the crumb aside for another use.
2. Microwave the butter and add a large pinch of salt for about 1 minute. Brush the inside and outside of the bread boxes with melted butter. Place 1 slice of cheese in the bottom of each box. Place the boxes open-side up on a baking sheet and bake until the cheese is melted and the inside of the bread is lightly golden and crispy, about 10 minutes.
3. Meanwhile, heat 1 tablespoon oil in a large skillet over medium-high heat. Pour 1/4 cup water into a small liquid measuring cup. When the oil begins to shimmer, add the onion and a large pinch of salt. Cook, stirring, until the onion is softened and lightly browned, 6 to 8 minutes. If the pan becomes too hot, add 1 tablespoon water and scrape up any browned bits from the bottom.
4. Add another 1 tablespoon of oil and the red and green bell peppers to the skillet. Season with a generous pinch of salt and cook, stirring, until the vegetables are tender, 6-8 minutes. Add the remaining oil and the roast beef and cook, stirring, until heated through, about 2 minutes. Turn off the heat and stir in the cheese sauce.
5. Evenly distribute the meat mixture among the bread boxes and top with 2 more slices of cheese. Return to the oven and bake until the cheese is melted, about 5 minutes. Serve the bread boxes whole or cut in half.