1) Make the sauce
In a small bowl, whisk together sour cream, mayonnaise, chipotle in adobo, adobo sauce, lime juice, and a pinch of salt. Taste and adjust. More lime for brightness, more chipotle for heat. Set aside.
2) Season and cook the steak
Pat the steak dry. In a small bowl, mix salt, chili powder, cumin, smoked paprika, garlic powder, and black pepper. Rub the seasoning all over the steak.
Heat a large skillet over medium-high heat. Add 1 tablespoon olive oil. Sear steak 3 to 5 minutes per side depending on thickness, until nicely browned.
Temperature note: For medium-rare, pull the steak at about 125°F to 130°F, then rest. It should land around 130°F to 135°F after carryover cooking (thicker steaks carry over more). For medium, pull around 135°F to 140°F. For medium-well, pull around 145°F.
Transfer to a cutting board and let rest 5 to 10 minutes. Slice very thin against the grain. If you are using flank or skirt, think almost shaved. It eats more tender that way.
3) Sauté peppers and onions
In the same skillet, add a little more oil if needed. Add the sliced pepper and onion with a pinch of salt. Cook 4 to 6 minutes, stirring, until softened but still a little crisp.
Add the lime juice in the last 30 seconds (or off heat) to deglaze without over-softening the veggies. Scrape up any browned bits, then turn off heat.
4) Assemble
This recipe is written for 4 folded quesadillas (one tortilla each). If you prefer the stacked, two-tortilla style, use 8 tortillas and divide the filling across 4 quesadillas.
Wipe out any excess liquid in the skillet if needed and return it to medium heat. Lay one tortilla down. Sprinkle a light layer of Monterey Jack, then add a quarter of the steak and a quarter of the pepper-onion mixture. Top with a mix of Jack and cheddar, then fold the tortilla in half.
Tip: Cheese on the bottom and top acts like edible glue. That is how you keep the inside from sliding around when you slice.
5) Cook until crisp and melty
Cook 2 to 3 minutes per side, pressing gently with a spatula, until deep golden and crisp.
If you want extra browning and that cozy diner-style flavor, add about 1/2 teaspoon butter to the pan right before cooking the second side. A little goes a long way.
Repeat with remaining tortillas and filling.
6) Slice and serve
Rest each quesadilla 1 to 2 minutes so the cheese sets slightly, then slice into wedges. Serve with the lime chipotle sauce, plus salsa or guacamole if you have them.
