Heat milk until it is nearly boiling (a double boiler is safest). Mix sugar, flour, and beaten eggs together. Remove milk from heat and stir 1 ladle full into the sugar mixture to temper the eggs. Add the tempered egg mixture into the hot milk. Return to low heat and stir until mixture begins to thicken. When cool, add vanilla. Strain through a wire strainer to remove any lumps. Whip whipping cream and add sugar to taste, put aside. Grate fresh nutmeg and put aside, this will also be used to top dessert once complete.
Cream sugar and butter. Add egg yolks 1 at a time. Mix the flour and baking soda together. Add sour cream and flour, alternating to the butter and sugar. Beat egg whites stiff and fold in. Pour into greased and floured tube cake pan. Bake at 300 degrees F. in a preheated oven for 1 1/2 to 1 3/4 hours. Invert immediately into a glass serving bowl and drizzle with Sherry. Pour custard on top, and then add already made whipping cream. Top with freshly grated nutmeg.