This unique delicacy was for years a closely guarded secret, the recipe being given out only to family members. The cake actually improves with age, being better a few days after it is baked; the flavor is enhanced, and the sliver-thin layers take on a slightly chewy texture. Although it can be made in the regulation two or three layers, it is much the best when made in six very thin layers–spread evenly in the pans to a thickness of about a quarter inch.
Cream the butter and sugar. Break the egg into a cup measure and fill the cup with sour milk. Add to the butter and sugar. Add the other ingredients and beat well. Four the batter very thinly in greased cake pans, just covering the bottom (use a spatula to make sure the batter lies evenly over the bottom). The recipe will make 3-6 layers, depending on thickness. Bake in a moderate oven (350 degrees F) until the edges are brown and drawn away from the side of pan. While the cake is baking, whip the currant jelly with a fork until liquid. When the cake is cool, spread the top of each layer with jelly. Dust top with powdered sugar.