1Preheat your oven broiler to high and position the oven rack about 6 inches from the heat source. While the broiler heats, prepare your bolillos or bread. If using traditional bolillo rolls, slice them in half horizontally to create two open-faced pieces from each roll. If using a small baguette or French bread, cut it into 6-inch sections, then slice each section in half lengthwise. The goal is to have pieces that are about 6 inches long and flat enough to hold toppings. The cut side should be relatively flat - if your bread is very crusty or rounded, you can press down gently or trim a thin slice from the bottom so it sits flat on the baking sheet.
2Spread the softened butter evenly over the cut sides of the bread. The butter adds flavor and helps the bread toast to a golden brown. Place the buttered bread slices cut-side up on a large baking sheet. Toast under the broiler for 2-3 minutes, watching carefully, until the bread is lightly golden and crispy on top. The bread should be toasted enough to provide a crunchy base that will not get soggy from the beans, but not so dark that it is burnt. Remove from the oven but leave the broiler on. This pre-toasting step is important - it creates a barrier that prevents the beans from making the bread soggy.
3If your refried beans are cold from the refrigerator, warm them slightly in a small pot or microwave until they are spreadable but not hot - you want them warm enough to spread easily but they do not need to be piping hot since they will warm more in the oven. Spread a generous layer of refried beans evenly over each toasted bread half, covering the surface completely from edge to edge. Use about 1/4 cup of beans per half, or more if you prefer. The layer should be substantial - about 1/4 to 1/2 inch thick. The beans are the foundation of the mollete and should be plentiful. Make sure to spread them all the way to the edges so every bite has beans.
4Sprinkle the shredded cheese generously over the beans, covering them completely. Use about 1/4 cup of cheese per half, or more if you are feeling indulgent - molletes should be cheesy. Oaxaca cheese is traditional and melts beautifully with a stringy texture similar to mozzarella. If you cannot find Oaxaca cheese, Monterey Jack, Chihuahua cheese, or even mozzarella work well. Some people like to mix different cheeses for more complex flavor. Make sure the cheese covers the beans completely - you should not see much bean showing through. The cheese will melt and bubble beautifully under the broiler.
5Return the topped molletes to the oven under the broiler. Broil for 3-5 minutes, watching very carefully, until the cheese is completely melted, bubbling, and developing golden brown spots on top. The cheese should be gooey and slightly browned - those browned bits add incredible flavor. Watch closely as broilers vary in intensity and the cheese can go from perfectly melted to burnt quickly. If some molletes are browning faster than others, rotate the pan or remove the done ones while the others finish. The goal is melted, bubbly cheese with some caramelized spots but not burnt. Remove from the oven once the cheese reaches this perfect state.
6Transfer the hot molletes to serving plates. Top each one with a generous spoonful of fresh pico de gallo - the cool, fresh tomato salsa provides essential brightness and acidity that balances the rich beans and cheese. If using, add pickled jalapeños for heat and tanginess. Drizzle with Mexican crema or a dollop of sour cream - the cooling dairy contrasts beautifully with the hot, melted cheese. Garnish with fresh cilantro leaves and serve with lime wedges on the side. Squeeze lime juice over the molletes just before eating for extra brightness. Molletes are best enjoyed immediately while the cheese is still hot and gooey and the bread is crispy. Serve with hot coffee or fresh fruit juice for a traditional Mexican breakfast. They can also be served as a light lunch or dinner, or as an appetizer cut into smaller pieces. The combination of crispy bread, creamy beans, melted cheese, and fresh toppings is irresistible.