The easiest answer would be to use a soy sour cream, even though it can be hard to find. But that may not solve your problem. Soy-based sour creams can be certified kosher pareve because they contain neither meat nor dairy. But soy is not universally regarded as kosher for Passover.

Kosher for Passover is essentially a subset of kosher in Orthodox Judaism that excludes grains. Wheat, rye, barley, and certain other grains that might have come in contact with water after harvest might have begun to ferment – a step in the leavening process – rendering them not kosher for Passover. Matzo, the bread/cracker that symbolizes Passover, which is most often made of wheat flour, is made under strict conditions to ensure that it is completely unleavened.

What does that have to do with soy, you ask, which is a legume and not a grain? Taking it one step further, some Ashkenazi Jews also consider legumes, rice, and corn (and all derivative products) outside the realm of acceptable foods for Passover. (Coca-Cola makes a version of Coke with sugar instead of corn syrup during Passover, and a number of other companies modify certain products to be acceptable during the holidays.)

So if soy sour cream is out for Passover, we would not try to find another substitute for the sour cream, we would find another brownie recipe that doesn't include dairy ingredients. There are only about 77,614 to choose from and 1,846 of them are really good.

Hey! Here's one….