Substitute for ragu in kosher lasgne

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.

By "Italian Sausage" I think you mean the seasoned pork sausage available in many supermarkets throughout the US.

I've found that a 30-70 mix of beef and turkey/chicken works reasonably well as a substitute when pork is not available. Beef is too strong a flavor and turkey too weak in its own. Flavor-wise most italian sausage has red wine, fennel, and oregano.