The day before, place the Dried Tolosa Beans (Alubia de Tolosa) in a large bowl or pot and cover with plenty of cold Water; soak for at least 8–12 hours, then drain and rinse well.
Put the soaked beans into a heavy-bottomed pot and cover with fresh Water so the level is about 3–4 cm above the beans; bring to a gentle boil, skim off any foam, then reduce to a low simmer.
While the beans are coming up to temperature, warm 2–3 tablespoons of Olive Oil in a skillet over medium heat.
Add the chopped Onion, diced Green Bell Pepper, and minced Garlic to the oil and sauté until soft and translucent, about 6–8 minutes, creating a flavorful sofrito.
Stir in the diced Panceta (salt pork/bacon) and cook until it releases some fat and begins to brown; then add slices of Spanish Chorizo and a couple of whole Ibarra Guindilla Peppers to the pan and sauté briefly to awaken their flavors.
Transfer the sofrito and meats into the pot with the simmering beans, bring back to a gentle simmer, cover partially, and cook very gently for 1½–2 hours, checking occasionally and adding a little extra Water if the stew becomes too dry.
About 15 minutes before the end of cooking, tuck in the whole Morcilla de Cebolla (Basque blood sausage) so it warms through without breaking apart; taste and season with Salt toward the end of cooking (salting early can toughen bean skins).
If you prefer a thicker broth, mash a cupful of beans against the side of the pot with a spoon and stir to incorporate—this will naturally thicken the stew and make it silkier.
Remove the whole guindilla peppers if you don’t want too much heat, adjust seasoning, and let the stew rest for 10 minutes off the heat so flavors meld.
Ladle the Alubias de Tolosa into bowls and serve with plenty of Crusty Bread for sopping up the rich broth, and enjoy warm.
