To a large pan, off the heat, add the guanciale then set over medium heat. Slowly render out the fat from the guanciale until it is crispy. Use a slotted spoon to remove the guanciale and set on a paper-towel lined plate to the side, leaving all of the fat in the pan. Turn off the heat and set this pan aside temporarily.
In a separate small pan, quickly toast the breadcrumbs. Spoon about 1 tablespoon of the rendered guanciale fat into the small pan and leave the rest undisturbed in the main pan, along with 1 teaspoon of the oil from the jar of calabrian chilies. Over medium heat, add the panko to the small pan. Stir continuously until golden and fragrant, adding more oil if needed. Once golden and crispy, season with a small pinch of salt and set to the side.
Place the large pan back over medium heat, then add the garlic and saute until fragrant, but not browned. Add in 1½ tbsp of chopped calabrian chilies and stir, then lower the heat.
Meanwhile, bring a large pot of salted water to a rolling boil. Drop in the pasta bowties and boil until they float to the top. Reserve about 1/2 cup pasta water.
Return the pan to medium heat. Add a generous splash of pasta water and let it simmer, scraping up any bits from the bottom. Add the pasta, at least 3 bowties at a time. (Work in batches if needed). Add the cold butter cubes and half of the guanciale and swirl the pan vigorously, until the sauce is glossy and coats the pasta. Taste and add salt as needed. Repeat with the second serving of 3 bowties if necessary.
Plate 3 bowties per serving, spooning extra sauce over the pasta and topping with the toasted panko breadcrumbs and remaining guanciale pieces.