In a large pan, heat the oil and butter on medium heat. Add the onion, bell and pepper. Cook until the vegetables begin to soften. Add the tomato. Cook for about 30 additional seconds. Set the vegetable mixture aside in a small bowl or plate.
Heat some additional oil and butter. Add one of your tortillas.
Pile on the white cheddar cheese. Make sure you have enough cheese to get close to the edges of the tortilla. The cheese will act as the glue to keep you quesadilla together. If you like cheese as much as I do, you can be generous with the cheese.
Add the cooked steak and vegetables. Top with more white cheddar, and (if you like) a little of the Roquefort or Gorgonzola.
At this point, check to see if the bottom half has crisped up to your liking. If it has, the quesadilla is ready to flip over. Using a large spatula, flip the quesadilla over. Cook the bottom part until the desired crispness, and you are almost ready to serve.
Slide the quesadilla onto a wooden cutting board and cut into sections.
Serve with sour cream and guacamole.