I find it annoying too that recipes come in 4 blocks when I eat three. However, 12 is divisible by both 4 and 3, so what I do is triple a 4-block recipe to make 12 blocks. Then I eat a 1/4 portion of the prepared food to get 3 blocks.
Unfortunately, it's all about math! Hard to believe that our 7th grade teachers were right and that stuff would actually be useful someday, LOL....