In a cast iron skillet or heavy bottomed pan, add the sugar and melt over medium to medium high heat. Don’t stir, just let the sugar melt and turn a deep caramel brown color, 3-5 minutes.
Add the pork belly, stir and cook until lightly golden brown, about 5 minutes.
Stir in the the water, fish sauce, onions and shallots. Bring to a boil and then reduce the heat until the liquid is at a simmer.
Simmer, stirring occasionally, until tender and the sauce reduces greatly, about 20-30 minutes.
Meanwhile, bring a large pot of salted water up to a boil and cook the spaghetti according to the package time. When done, drain and do not rinse. Add the pasta directly into the pan and toss to coat.
Taste and season with plenty of black pepper. Enjoy immediately!
Notes
Different fish sauces have different saltiness levels. If you’re not familiar with your bottle, start with 1-2 tablespoons of fish sauce and season to taste.