Over an open fire or in a high oven, roast jalapeño and poblano chiles until the skins are evenly charred. Remove and discard the skins and seeds; dice the peppers, and set aside. In a water bath, melt cheese product and milk until combined, about 15 minutes. Add onion and diced roasted peppers, and cook 10 to 15 more minutes. Add vinegar and salt. Garnish, if desired. Serve warm with warm tortilla chips.