To make the beans: Add pinto beans, garlic cloves, onion, salt and oregano to a medium saucepan. Cover with about 2 inches of water. Bring water to a boil, then turn down to a simmer. Cover and cook beans for 2 hours, or until very tender.
Strain cooked beans from the bean juice and reserve the juice for later.
In a large skillet over medium-high heat, add 4 tbsp lard and the beans. Fry up the beans for about 2-3 minutes, stirring constantly.
Reduce heat to low and add bean juice to the skillet (should be about 1/2-3/4 cup juice). Begin to smash beans using a potato masher until you reach your desired consistency. If you like your beans very smooth with no chunks of beans, place in a blender and blend until smooth. Add a little bit of water, about 1 tbsp at a time, if your beans are too thick.
Heat 4 flour tortillas on a large skillet over high heat for 30 seconds on each side.
To assemble burritos: Place about 3/4 cup of refried beans in the center of a hot tortilla. Top beans with 1/8 cup cotija cheese and fold burrito. Top with sour cream, your favorite salsa and guacamole. Repeat with all four burritos!
Serve with tortilla chips if you'd like! Enjoy!