In a small bowl, pour sherry over raisins, and let soak. Set aside.
Spray 2 (9-inch) cake pans with baking spray with flour. Set aside.
In a large bowl, combine cake mix, eggs, water, sour cream, oil, and lemon zest. Beat at low speed with a mixer for 30 seconds, scraping sides of bowl as necessary. Increase speed to medium, and beat for 2 minutes. Divide batter evenly between prepared cake pans. Tap pans on countertop to reduce air bubbles.
Bake until layers are light golden brown and a wooden pick inserted in the centers comes out clean, approximately 20 minutes. Let cool in pans for 10 minutes. Turn out layers onto wire cooling racks, and let cool completely.
In a medium saucepan away from heat, combine egg yolks and sugar, stirring until smooth. Add melted butter, transfer saucepan to stovetop, and cook over medium heat, stirring constantly, until mixture coats the back of a spoon, 5 to 6 minutes. Do not let egg mixture boil.
Add pecans, coconut, dates, and raisins with sherry, stirring to blend. Cook for approximately 1 minute.
Add vanilla extract and salt, stirring to blend. Remove saucepan from heat, and let fruit mixture cool to lukewarm.
Place each cake on a serving plate. Spread half of fruit mixture on top of each cake, leaving a ½-inch border around edge. (This is where frosting will be piped).
Using an offset spatula, spread Vanilla-Marshmallow Frosting around sides of cakes. Place remaining frosting in a piping bag fitted with a medium open-star tip (Wilton #21). Pipe a decorative shell border around edge of cakes.
Serve immediately, or store, lightly covered, in the refrigerator for several hours. Let come to room temperature before serving.