A long cooking time softens pinto beans; their mellow flavor is emboldened by bits of smoky bacon. A sprinkle of chopped, fresh sage added at the last minute brightens the dish.
Place beans in a large bowl, and cover with water by 2 inches. Loosely cover, and soak in the refrigerator overnight.
Preheat oven to 375 degrees. Drain beans. Melt butter with oil in a large saucepan over medium-high heat. Reduce heat to medium, and add onion, garlic, and bacon. Cook, stirring occasionally, until bacon is translucent, 4 to 5 minutes.
Stir in stock, beans, and sage. Bring to a boil; cover, and transfer to the oven. Bake until beans are tender, about 1 hour 45 minutes. Season with salt and pepper, and garnish with chopped sage.