Butternut Squash Sandwich with Cheddar Cheese and Pickled Red Onion

Ingredients

• 1 medium butternut squash (about 2 pounds)
• 1/4 cup extra-virgin olive oil
• 8 sprigs thyme
• 2 garlic cloves, smashed
• 1 3/4 teaspoons kosher salt, divided
• 1/2 teaspoon freshly ground black pepper
• 1/4 cup red wine vinegar
• 1 1/2 teaspoons sugar
• 1/2 medium red onion, thinly sliced
• 1/4 cup mayonnaise
• 2 tablespoons Dijon mustard
• 4 ciabatta rolls
• 4 slices white cheddar
• 1 cup arugula
• Chips (for serving; optional)

Directions

1. Arrange racks in middle and upper thirds of oven; preheat to 450°F. Cut squash in half crosswise where the neck and body meet. Peel and seed. Slice neck lengthwise into 1/4"-thick planks (about 2 1/2" long). Slice body into 1/4" pieces.
2. Divide squash, oil, thyme, garlic, 1 tsp. salt, and 1/2 tsp. pepper between 2 rimmed baking sheets. Toss to combine, then arrange in a single layer. Bake, tossing once halfway through and rotating trays, until squash is tender, 18–20 minutes.
3. Meanwhile, bring vinegar, sugar, remaining 3/4 tsp. salt, and 1/2 cup water to a boil in a small saucepan. Remove from heat, then stir in onion. Let cool.
4. Whisk mayonnaise and mustard in a small bowl. Remove thyme leaves from stems, then finely chop leaves and garlic. Stir into mayonnaise mixture.
5. Slice rolls in half and toast in oven 5 minutes. Spread 2 Tbsp. mayonnaise mixture on bottom halves. Top each with squash, cheese, 1 1/2 Tbsp. pickled red onion, and arugula. Serve with chips alongside, if using.
6. Squash can be roasted 3 days ahead; cover and chill. Onions can be made 1 month ahead; cover and chill.