Make the cilantro cream: Puree the sour cream, cilantro, lime juice and hot sauce in a blender until smooth.
Prepare the quesadillas: Mix the meatloaf, beans, scallion, cumin, cayenne, and salt and black pepper to taste in a bowl.
Melt 1/2 tablespoon butter in a large nonstick skillet over medium-high heat. Place a tortilla in the pan, sprinkle with 1/4 cup cheese, then top with one-quarter of the meat mixture and another 1/4 cup cheese. Top with another tortilla and cook until golden, about 2 minutes per side. Repeat with the remaining butter, tortillas and filling. Cut the quesadillas into wedges and serve with the cilantro cream.