1 pound skirt steak, cut widthwise into 6- to 8-inch pieces
1 chipotle in adobo sauce, finely chopped
Kosher salt& freshly ground black pepper
Vegetable oil for oiling the grill
12 ounces Monterey Jack cheese, shredded on the large holes of a box grater and
4 ounces sharp cheddar cheese, shredded on the large holes of a box
8 (10-inch) flour tortillas
Salsa, Guacamole and Sour cream, for serving
Heat an outdoor grill to high (about 400°F to 500°F). Pat the steak pieces dry with paper towels and lay flat. Brush the chipotle on one side of the steak pieces. Season both sides of each piece generously with salt and pepper.
When the grill is ready, use tongs to rub the grate with several layers of paper towels dipped in vegetable oil. Place the steak pieces on the grill and cook until medium rare, flipping halfway through the cooking time, about 5 to 6 minutes total. Remove to a cutting board and let rest for 2 minutes. Cut into medium dice and set aside.
Combine the cheeses in a medium bowl. Place 2 tortillas side by side on a clean cutting board or 2 plates. Sprinkle each tortilla with a quarter of the steak and cheese mixture. Top each tortilla with another tortilla and gently press down.
Carefully slide the quesadillas from the cutting board or plates onto the grill. Cover the grill and cook, rotating 90 degrees halfway through the cooking time, until the cheese is completely melted, the tortillas are crispy, and grill marks have appeared on the bottom, about 3 to 4 minutes total. Using a spatula, carefully flip the quesadillas over and repeat cooking and rotating until the bottom tortillas are crispy, about 2 to 3 minutes more. Using a spatula, transfer the quesadillas to a cutting board and let rest for 2 minutes. Repeat with the remaining tortillas and filling to make 2 more quesadillas.
Cut each quesadilla into wedges and serve with salsa, guacamole, and sour cream.