This is the same technique I used for the black bean recipe I posted earlier. The main difference is that I do not prefer to use epazote/Mexican oregano with pinto beans because it obscures their more delicate flavor too much. I love the texture these beans get when they're cooked this way.
1 lb. dried pinto beans, sorted and rinsed and soaked in filtered water for 4-6 hours
1-2 large white onions, halved and thinly sliced
3-4 bay leaves
1 Tbsp. sea salt
1) Spread the beans out on a dark colored kitchen towel (something not similar to the color of the beans so that you can see them better) and sort through them for broken or malformed beans and foreign matter.
2) Place the beans in a colander and run them under cold water as you rub them together to wash. Then place them in a large glass bowl and cover them with 2-3 inches of water and let them soak for 4-6 hours, adding more water if they absorb it all.
3) Place the beans back into the colander to drain them and then rinse them off again. Place them in a large dutch oven or pot and cover them with 2-3 inches of fresh water along with the sliced onions and bay leaves and bring to a boil
4) Once the liquid has come to a boil, reduce the heat to a level where it remains at a low boil (more than a simmer). Let them cook this way for about an hour while stirring occasionally and adding more water if they start to dry out.
5) After an hour test a couple of beans and if they are mostly soft add 1 Tbsp. of salt (if not let them go for another 1/2 hour and test again). Continue to cook for an additional hour, adding more water when necessary and stirring occasionally to ensure they don't stick and burn.
6) Once the beans are completely soft, quit adding water and let the liquid evaporate (stirring more frequently at this point) until they are in a thick sauce.
Serve with cooked grains and a little salsa, in tacos or burritos, or use them to make a batch of Pinto Bean Enchiladas.
This makes a lot of beans.