Add chilis, garlic, and shallots to a sheet pan and broil until charred.
Remove from oven and let cool for 5 minutes before peeling the skins off of all ingredients.
They should slide off easily.
Add to a blender along with fish sauce, brown sugar, lime juice, cilantro, and coriander seeds.
Blend until thoroughly mixed but still coarse in consistency.
While blender is running, slowly add oil to create an emulsion.
This mixture will keep in the fridge for up to a week.