Split cake in half crosswise. Spread cut side of bottom half of cake with jelly; cover with cut side of top. Press almonds and citron randomly into top of cake.
Transfer cake to a trifle or other decorative bowl; pour wine evenly over prepared cake. Cover and refrigerate overnight.
Combine 1/2 cup sugar and 3 cups milk in top of a double boiler. Place over boiling water, stirring until sugar dissolves.
Combine remaining 1/4 cup sugar, 1 cup milk, eggs, flour, and soda in a medium mixing bowl. Gradually add to milk mixture in top of double boiler, stirring constantly. Cook over boiling water, stirring constantly, 20 minutes or until mixture thickens and coats a metal spoon. Stir in vanilla. Remove from heat, and cool.
Pour custard over prepared cake in bowl. Chill thoroughly before serving.