For the sponge cake:
For the filling:
Begin early in the day or the day before serving.
Preheat oven to 375º F.
Grease bottoms of two 9-inch round cake pans and line with waxed paper. Sift flour, baking powder and salt. In a medium bowl at high speed, beat 4 egg yolks, ½ cup sugar and ½ teaspoon vanilla extract just until thick. In a separate bowl with a mixer at high speed, beat egg whites until soft peaks form; gradually sprinkle in 6 Tablespoons sugar, beating until sugar is dissolved and whites stand in stiff glossy peaks.
Sprinkle flour mixture over beaten yolk mixture in medium bowl.
Add beaten egg whites to mixtures in medium bowl, then with rubber spatula, gently fold in until blended. Spread batter evenly in pans.
Bake 15 minutes until top springs back when touched with finger. Cool in a pan on wire rack for 10 minutes; remove from pan and cool on wire rack.
For the filling:
With knife, cut cake horizontally in half, spread lower half with cranberry mixture and replace top.
Cut layers into bite-sized pieces and place first layer randomly in bottom of deep, 3 quart glass bowl.
Sprinkle with one half the amount of sherry and top with half of the crushed macaroons.
In a 2-quart saucepan bring the milk and lemon zest to just below the boiling point, remove from heat. In a medium bowl, beat the egg, egg yolks and sugar until creamy. Add the flour and vanilla as you beat with a whisk, then slowly beat in the hot milk, whisking all the while. Pour this mixture into the pot in which you heated the milk. Cook over medium heat, stirring until thick, about 5 minutes. Remove from heat.
Pour one half of the custard over cake pieces in bowl. Top with the remaining cake pieces, the rest of the sherry and all but 2 Tablespoons of crushed macaroons (reserve these for the topping.) Then pour the other half of the custard over the top and spread out evenly. Sprinkle the reserved crushed macaroons over the custard surface. Cover surface with plastic wrap and refrigerate about two hours.
Spoon whipped cream into pastry bag fitted with a large rosette tube. Decorate the top of the custard. Garnish with the candied red cherries and the toasted slivered almonds.