Here are three ways to thicken the gravy.
1. Strain the solids, reserve them, reduce the gravy, and return the solids to the pot. Or, just reduce as you cook.
2. Make a slurry with masa or flour and water. Add the slurry to the stew, bring to the boil until thickened (around three minutes) reduce the heat to a simmer and continue cooking until the "raw" is off the flour. About ten minutes.
3. Make a slurry with arrow root, and thicken accordingly. Arrowroot which is desirable in many ways, will not hold for long. I doubt corn-starch will work well as chile verde is too acid.
My preference would be to combine reduction with a masa slurry; and to get the slurry in the stew just as the tomatillos fully melt, before the meat is completely cooked.
If it's necessary for you to puree the tomatillos
, you're missing something very basic about chile verde. Here's an excellent chile verde recipe: http://www.cheftalk.com/forums/recip...-approval.html
If you try it, please let me know how it works for you.