Prepare the casings: rinse the Pork Large Intestines (hog casings) thoroughly under cold running water, turn them inside out and flush the interior until clear. Soak the casings in warm water for at least 30 minutes, then keep them in cold water until ready to stuff.
Cook the rice: rinse the Short-Grain Rice under cold water until the rinse runs clear. Cook the rice in a pot of boiling Water salted lightly until just tender but still holding its shape (slightly undercooked is OK because it will finish setting later). Drain and spread on a tray to cool and lose excess moisture.
Make the onion and fat base: finely chop the Large White Onions and dice the Pork Back Fat. In a large skillet, render the fat over medium heat, then add the onions and cook slowly until soft and beginning to caramelize. Season the mixture with a good pinch of Fine Sea Salt, freshly ground Ground Black Pepper and stir in the Sweet Paprika for a minute to bloom its flavor. Let this mixture cool slightly.
Combine the filling: in a large bowl, fold the cooled rice and the onion–fat mixture together. Gradually pour in the Fresh Pig's Blood, stirring constantly to achieve a cohesive, moist mixture—stop when the mix holds together but is not soupy. Taste and adjust seasoning with more salt, pepper or paprika as needed. If the mixture feels too loose, add a little more cooked rice.
Stuff the sausages: fit a casing onto your sausage stuffer or a funnel and gently fill with the blood–rice mixture, avoiding large air pockets; leave some casing slack and tie off into links of your desired length. Prick any obvious large air bubbles with a needle to prevent bursting during cooking.
Poach the sausages: bring a large pot of water to a gentle simmer (do not boil vigorously). Submerge the sausages and poach at a low simmer for about 30–45 minutes depending on their thickness; keep the water just below a rolling boil so the casings do not split.
Cool and finish: transfer the cooked morcillas to an ice bath to stop cooking and help them firm up. Once cool, pat dry and refrigerate for a few hours or overnight to set the texture. To serve, slice and pan-fry the slices in a little oil until browned and crisp at the edges, or grill gently and serve warm.
