Put the chilies, cloves, peppercorns, and cumin seeds in a small frying pan. Toast over medium heat just until fragrant, 2-3 minutes, then immediately pour onto a plate and let cool.

Scrape the ginger with a spoon to remove peel, then coarsely chop. Coarsely grind the toasted spices in a spice grinder or clean coffee grinder. Transfer the ginger, ground spices, vinegar, garlic, red pepper flakes, garlic salt, and turmeric to a blender. Grind into a coarse paste, scraping down the sides as needed.

Cut the pork shoulder into 1/2-inch chunks and transfer to a medium mixing bowl. Add the masala paste and massage into the pork. Cover and refrigerate for at least 1 hour or overnight.

Roughly chop the onion. Heat the oil in a Dutch oven over medium-high heat. Add the onion and stir well, then add the sugar and salt. Cook, stirring often, until onion begins to turn golden, about 10 minutes.

Add the pork and its marinade and increase heat to high. Cook, stirring occasionally, until meat is browned, about 5 minutes. Reduce heat to low, cover, and simmer, stirring every 8-10 minutes, until pork is tender and the vindaloo gets a thick, jam-like consistency, 45-60 minutes total. During cooking if the vindaloo starts to look like it could scorch, add up to 1/2 cup water.

Serve the vindaloo with steamed basmati rice or naan.