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1
Render a little fat in a heavy pot over medium heat. Add the garlic and cook until pale gold and fragrant. Add the pork shoulder cubes and sear until the surfaces are opaque and beginning to colour — the meat should show no raw pink on its exterior.
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2
Pour in the vinegar and allow it to cook uncovered without stirring for 2 minutes so the acid integrates and its sharpness mellows. Add the pork broth and long green chillies. Simmer, partially covered, until the shoulder is tender enough to yield to light pressure — approximately 25–30 minutes. The offal cooks faster: add intestine and kidney only in the final 10 minutes of this stage to prevent them overcooking.
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3
Reduce the heat so the liquid is at a bare simmer — no violent boil. Pour in the fresh pig's blood in a steady stream while stirring constantly with a wooden spoon. Continue stirring without pause for the first 5 minutes: this is where the dish lives or dies — constant agitation prevents large clots from forming as the blood proteins coagulate, and the vinegar already in the pot holds the proteins back from over-setting, producing a smooth, dark, unified sauce rather than a grainy one.
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4
Season with fish sauce. Continue to cook at a gentle simmer, stirring regularly, until the sauce reduces to a consistency that coats the back of a spoon and flows slowly when the spoon is tilted — watery sauce requires further reduction. The colour should be a deep, almost-black mahogany.
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5
Remove from heat. Stir in the pork lard: it melts into the surface of the sauce, creating an unctuous gloss and rounding the iron sharpness of the blood. Taste and adjust with additional fish sauce or vinegar. Serve immediately with puto or white rice.