In a bowl, combine pork blood and vinegar. Stir until smooth, mashing any lumps with a spoon. Set aside.
In a pot over medium heat, cook pork with a splash of water until the fat renders and the pork lightly browns. Season with salt, transfer to a plate, and discard excess fat.
In the same pot, add oil as needed. Sauté ginger, onion, garlic, and chilies until softened.
Return the pork to the pot. Slowly pour in the blood mixture while stirring to keep it smooth.
Add coconut milk and lemongrass. Bring to a boil.
Cover and simmer over medium heat for about 45 minutes, or until the pork is tender and the sauce thickens. Stir occasionally.If using chayote, add it after 30 minutes and cook until tender.
Season with fish sauce, salt, and pepper. Add a little water if too thick. Remove lemongrass and turn off the heat.
Notes
Pork blood: Usually sold frozen. Thaw completely before using.
Pork belly: You can also use pork shoulder or add innards.
Vinegar: Keeps the blood smooth and adds tangy taste. Tamarind, calamansi, or kamias also work.
Coconut milk: Makes the sauce a little creamy and less sharp.
Lemongrass: Optional, but helps with the strong smell and adds a light citrus taste.
Chayote: Optional, if you want some vegetable in the stew. It stays firm.
How to Store and Reheat
Store: Refrigerate for up to 3 days.
Freeze: Freeze for up to 2 months; thaw overnight in the fridge.
Reheat: Microwave or warm over low heat, adding a little water if too thick.