Make the Nacho Cheese Sauce: Melt butter in a saucepan over medium heat. Whisk in flour and cook for 2-3 minutes. Slowly add milk, whisking until smooth. Cook until thickened. Lower heat and stir in cheese until melted. Add pickle juice (or vinegar), jalapeño purée, chili powder, and paprika. Stir until combined and keep warm. Season with salt if needed, to taste.
Cook the Beef: In a skillet over medium heat, cook the ground beef until browned. Drain excess grease, then stir in taco seasoning with a little water. Simmer until thickened, then remove from heat.
Prep the Toppings: Dice the tomatoes, shred the lettuce, and set out the sour cream. If using shredded cheese instead of nacho cheese sauce, shred it now.
Assemble the Crunchwrap: Lay a large tortilla flat. In the center, layer in this order: seasoned beef, nacho cheese sauce (or shredded cheese), tostada shell, shredded lettuce, diced tomatoes, and sour cream.
Fold the Crunchwrap: Start at the edge of the tortilla and fold sections inward, working around in a circular motion to seal everything inside. Press down gently to hold its shape.
Toast the Crunchwrap: Heat a dry skillet over medium heat. Place the Crunchwrap seam-side down and cook for about 2 minutes until golden brown. Flip and cook the other side until crispy.
Slice and Serve: Transfer to a cutting board and slice each Crunchwrap in half before serving.
