Put the cheeses into a blender, and mash them down. You'll need to add milk to get them to blend. Add just enough so that they blend well. Then, put the spinach in in small clumps. Blend, and put more spinach in, until the whole bunch is gone. You'll have a nice green goo.
At this point, if you have a blender specifically for strong veggies, you can put the veggies in with the spinach. I put half the onion in before I realized that my roommate probably wouldn't like her shakes flavored with the faint taste of garlic and onion; I then carefully picked the onion out. You can skip that step :*)
Pour the cheese mix into a medium saucepan. Mix the remaining ingredients in. Add milk to taste. Bring it slow boil, and cook until it's a little more liquidy than you want: it'll thicken as it cools.
Eat with dippin' chips. Tortilla chips work great, too. Also good on french bread. (Advice: make this just before the party. Otherwise, there won't be any left.)
Source: original recipe Posted on GEnie by J.STRATTON6 [Hostess Man], Oct 24, 1992 MM by Sylvia Steiger, GEnie THE.STEIGERS, CI$ 71511,2253, GT Cookbook echo moderator, net/node 004/005