1. Prepare the toppings first: dice tomatoes, chop lettuce, prepare guacamole, and chop cilantro. Place all toppings in individual bowls for a topping bar.
2. Heat refried beans over low heat, slowly, stirring often. When refried beans have reached desired temperature, cover pan with a lid and turn heat to lowest simmer possible to just keep warm.
3. Line a plate with several sheets of paper towel and set to the side of the stove.
4. Heat oil in a large frying pan to 350°F. Dip a corn tortilla in just a bit - if it bubbles and fries, the oil is ready. Fry corn tortillas one by one, flipping them after 30 seconds or so. They should be golden brown and crispy when removed from the oil.
5. Use tongs to remove the tortilla from the oil, letting excess drip down into the pan before placing the tortilla on the paper towels to drain. Repeat until all 8 tortillas are cooked.

To assemble the tostadas:

1. Take a cooked tortilla and spoon 2-3 tablespoons of refried beans on it.
2. Sprinkle with cheese, lettuce, and tomato.
3. Top with spoonfuls of guacamole and sour cream, and top that with chopped cilantro. Eat immediately.