Preheat oven to 325 degrees.
Generously grease and lightly flour a tube pan. Sift flour three times.
Cream butter with sugar until light and fluffy. Add eggs, one at a time. Beat only until each disappears. Blend in 1 cup flour followed by 1/2 cup whipping cream. Repeat with 1 cup flour and 1/2 cup whipping cream. Add remaining flour. Fold in vanilla.
Add batter to pan, level it and drop it flat on the counter to knock out the air bubbles. Place in center of the oven and bake for an hour and fifteen minutes, or until it's browned on top and begins to pull away from the sides of the pan.* Remove from oven. Wait ten minutes and invert on a cake plate. Do not cover until cool to touch.
Stir in cornstarch and salt into sugar.
In heavy pot or double boiler, add water, lemon juice and egg yolk. Put over high heat and stir in dry ingredients. Cook until you see a bubble or it thickens. Remove from heat, stir in finely grated lemon rind and butter. Cool and pour over cake.
In food processor or blender combine all ingredients except chocolate. Process until very smooth. Stir in chocolate. Cover and refrigerate until ready to serve.