In a medium (4 quart or larger) sauce pot, melt the butter over medium heat. When melted, add in the onion and cook for 3 minutes or until it starts to soften. Add in the garlic and spice pack, stir to combine, and let cook for another minute. Whisk in the flour until no white remains and let cook for about a minute or so, stirring often.
Whisk in one cup of the milk and let the mixture come up to a simmer. As it simmers, it will start to thicken. When it starts to thicken, stir in the drained chilies with tomatoes, and the chili. Lower the heat to very low and stir in the cheeses, one handful at a time. (Don’t dump in all of the cheese at once.) Stir in about half of the Chili Fixins sauce pack and the sour cream. Taste the cheese dip to see if needs more cheese added; thin out with some milk if needed. (Keep in mind that it will become thicker as it cools, so it may benefit from an extra 1/2 cup milk added.) Let simmer again until it is very warm and then remove from the heat.
Pour the cheese dip into a large serving dish (possibly even an oven or microwave safe one in case it needs to be rewarmed later). Pour a little of the rest of the sauce pack on top and swirl around with a spoon. Sprinkle chopped cilantro on top and serve warm with chips.
To reheat, bake in a 350 degree oven for 10-15 minutes or until very warm or microwave at half power at one minute intervals, stirring in between intervals.