Which thickeners work well with dairy

In regard to the issues you've had with the Toffutti Sour Supreme...wait until you take it off the heat and stir it in right before serving.

If it still breaks, then try stirring arrowroot powder, tapioca starch (avail. in Asian markets), or potato starch (about a tablespoon per cup of sour supreme) into it before adding to the stroganoff. These starches (amylopectin) have a lower gellation point than grain-based starches (flour, corn, rice) which are higher in amylose and require heating to a higher temperature for the starch granules to swell and pop, releasing their starch.

OR

Try this recipe for kosher beef stroganoff where they're using coconut milk for the kosher cream sauce and say that the coconut flavor doesn't come through in the finished dish.

First, start your Thai coconut curry sauce in a separate pot (i.e. the coconut milk and later the seasonings; no meat , no vegetables, etc.). Make sure to shake the can of coconut milk before opening to ensure it is not separated. Add 1/2 the can to the pot. Bring to boil, reduce temperature and allow the mixture to reduce to almost a paste like texture. This will allow the coconut flavors to intensify, and give you a thicker starting point.

The key is to reduce some of your sauce before cooking everything else; if you attempt to reduce your entire sauce with the vegetables, they will overcook because the process takes too long. Once reduced, add the other 1/2 of the coconut mixture. You end up with a very silky, smooth coconut sauce. Afterwards add your curry paste, fish sauce, sugar, Thai basil etc.