Step 1

Mix together the heavy cream with the milk kefir in a jar. The heavier the cream, the thicker your resulting sour cream will be. You can keep experimenting to get the consistency that you want with the cream you are using. If you want to end up with a thinner sour cream, you can also bring down the fat content of the cream by mixing it with some milk.

Step 2

The cream should immediately begin to thicken. At first, it won't be sour, but you could use it in place of mascarpone in recipes.

Step 3

To sour the cream, it needs to be fermented. Cover the jar, and allow it to rest at room temperature. At first, allow it to ferment overnight.

Step 4

In the morning, taste the kefir sour cream. If you want it to be sourer, leave it out to ferment longer.

Step 5

Once you've achieved the level of sourness that you want, use it right away or store it in the fridge for later. Storing it in the fridge will slow down the fermentation process and keep it from getting sourer as quickly.