Preheat the oven to 325. Grease and flour two tall 8” or 9″ round cake pans.
Beat together the butter, sugar, vanilla and salt until light and fluffy, about 4-5 minutes.
Add the eggs, one by one, allowing each to beat fully before adding another. Once all the eggs are in, beat for another 2 full minutes.
Sift in the cocoa, baking soda and flour and with the mixer on, pour the kefir in and mix until the batter is fully incorporated (scrape the bottom a few times to make sure nothing got stuck and didn’t blend). Avoid overbeating this once the flour is in the batter or the cake will come out tough.
Bake the cakes for 40-45 minutes, until a cake tester turns out clean or you can press the surface of the center of the cake and it springs back.
Let the cakes cool in the pan for 5-10 minutes, then flip them onto a wire rack to fully cool. Transfer to the freezer, wrapped tightly in plastic wrap, for an hour or more.
Frost the cakes when they are cold.