Cheesy Potato Quesadillas with Chipotle Mayo

• 12 ounces small red potatoes (5 to 7)
• 1 tablespoon kosher salt, plus more as needed
• 1/2 medium yellow onion
• 4 medium scallions
• 2 tablespoons olive oil, divided

Freshly ground black pepper

• 4 (about 6-inch) flour tortillas (often labeled fajita-style), divided
• 1 cup shredded Mexican cheese blend (about 4 ounces), divided
• For the chipotle sauce:
• 1/2 medium lime
• 1/2 cup mayonnaise
• 2 tablespoons canned chipotle in adobo sauce, plus more as needed
• 1/2 teaspoon kosher salt

1. Place 12 ounces small red potatoes and 1 tablespoon kosher salt in a medium saucepan and add enough cold water to cover the potatoes by about 1 inch. Bring to a boil over high heat. Meanwhile, thinly slice 1/2 medium yellow onion. Thinly slice the green and white parts of 4 medium scallions (about 3/4 cup).
2. When the water is boiling, reduce the heat to maintain a simmer. Cook until the potatoes are very tender, cooked through, and can be easily pierced with a sharp knife with no resistance, 15 to 20 minutes. Meanwhile, make the sauce.
3. Juice 1/2 medium lime into a medium bowl (about 1 tablespoon). Add 1/2 cup mayonnaise, 2 tablespoons canned chipotle in adobo sauce, and 1/2 teaspoon kosher salt, and stir to combine. Taste and stir in more chipotle in adobo sauce if desired.
4. When the potatoes are ready, drain. When cool enough to handle, transfer to a medium bowl and crush with the back of a fork or a potato masher into rough 1/2-inch pieces.
5. Heat 1 tablespoon of the olive oil in a large cast iron skillet or nonstick frying pan over medium-high heat until shimmering. Add the onion and scallions and cook, stirring occasionally, slightly charred, 5 to 6 minutes. Add the potatoes and cook, stirring halfway through, until lightly golden-brown, about 6 minutes total. Taste and season with kosher salt and black pepper as needed. Return the potato mixture to the bowl. Wipe out the pan with paper towels.
6. Place the pan over medium-low heat. Place 2 of the flour tortillas in the skillet in a single layer. Sprinkle 1/4 cup of the Mexican cheese blend onto one half of each tortilla. Top each portion of cheese with 1/4 of the potato mixture, then drizzle each portion of potato with 2 tablespoons of the sauce. Fold the other half of the tortillas over the filling and gently press down.
7. Increase the heat to medium high and cook, flipping once, until the quesadillas are golden-brown on both sides and the cheese is melted, 1 to 3 minutes per side.
8. Transfer to a cutting board. Add the remaining 1 tablespoon olive oil to the pan. Repeat assembling and cooking the remaining 2 quesadillas. Cut each quesadilla in half and serve with the remaining sauce on the side or drizzled on top.

Make ahead: The sauce can be made and the potatoes can be boiled up to 5 days ahead. Refrigerate in separate airtight containers.

Storage: Leftovers can be refrigerated in an airtight container for up to 4 days. Reheat the quesadillas in a low oven until warmed through.