Non-dairy creamer, dry

Crack the egg into a cup or bowl, whisk it, and measure out half of the contents. If you use eggs frequently, you could probably save the other half for a day or two – otherwise, it's like 8 cents out of your pocket.

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.