Cream butter, sugar and eggs. Sift flour, soda, baking powder and salt. Add flour mixture to creamed mixture alternately with buttermilk, starting and ending with flour. Beat until it is a creamy mixture. Bake in 3 round pans at 350 degrees for 25 to 30 minutes. Let cool 10 to 15 minutes. Make lemon filling. To make filling: In saucepan mix sugar, cornstarch and salt; add water, egg yolk and lemon juice. Cook over medium heat until it thickens, stirring constantly. Remove from heat and add butter. After cake is cooled, place the lemon filling on the first and second layers of the cake; sprinkle some coconut on top of the lemon filling. Put the third layer on top and ice with Seven Minute Frosting, or with a prepared commercial frosting. From A Taste of Louisiana. Downloaded from G Internet, G Internet.