Today, my mother, Mabel, would have been 105 years old. Usually I share one of my favorite pictures of the two of us, from a time before our family life together became so complicated. Today, instead, I am sharing one of the few things that I have in her own handwriting...the recipe for my favorite birthday cake, a cake which she made for me over and over again from a recipe she got from her mother during the Great Depression. In fact, it is sometimes called a depression cake, because it substitutes mayonnaise for eggs and oil, which were so difficult to find and so expensive to buy. Apparently Hellmann's…