Preheat oven to 350 degrees.

Place butter in an electric mixer. Add sugar slowly until well mixed. Slowly add eggs, beating after each addition.

Sift flour and mix with baking powder. Alternately add the flour mixture and buttermilk to the cake mixture. Combine well and stir in lemon zest. Bake in greased loaf pan for 1 1/4 to 1 1/2 hours. Remove from pan and cool.

Lemon Curd: Beat yolks well. Add lemon zest, juice and sugar over double boiler. Add melted butter and continue stirring. Cook until the curd coats the spoon and thickens. Refrigerate.

Custard: Dissolve the sugar in the creams over low heat. Beat the eggs and yolks well. Slowly add the warm cream.

Sauce: Warm butter in skillet and stir in brown sugar and lemon juice. Cook over medium high heat, stirring occasionally until bubbly. Add bourbon and return to a boil. Remove from heat and serve.

To Assemble: Lightly grease a 9 by 11 inch baking pan. Slice the cake into 1/4-inch slices. Place the cake slices over the bottom of the pan and spread with 1/2 of lemon curd. Repeat the 2 layers and pour custard over the top. Bake for 30 to 40 minutes Serve with Hot Toddy Sauce.