Recipe: Raspberry-Lemon Easter Cake - ISO: How to convert this cake to a sheet cake

My daughter's 21st birthday is Feb 21 and she has asked for a Raspberry-Lemon Cake. The recipe that follows is from Food Network and is for a layer cake. I need a cake to serve 30+ people, so a sheet cake is a must. Does anyone know how to convert this recipe to a sheet cake, and do you have any suggestions as to filling/icing the cake? Thanks.

RASPBERRY-LEMON EASTER CAKE

CAKE:
3 cups cake flour
2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon fine salt
1 1/4 cups sour cream
1/4 cup freshly squeezed lemon juice (about 1 1/2 lemons)
1 tablespoon pure vanilla extract
1 cup (2 sticks) unsalted butter, room temperature, cut into small pieces
2 cups sugar
1 teaspoon finely grated lemon zest
5 large eggs, room temperature
ICING AND FILLING:
1 1/4 cups sugar
5 large egg whites
1 1/2 teaspoons freshly squeezed lemon juice
1/4 teaspoon cream of tartar
Pinch fine salt
1 1/2 cups (3 sticks) unsalted butter, room temperature, cut into small pieces
TO ASSEMBLE:
1/2 cup seedless red raspberry jam
Candied almonds
Pastel sanding sugars

FOR THE CAKES:
Position a rack in the lower third of the oven and preheat to 350 degrees F. Lightly brush 2 (9-inch) round cake pans with shortening or butter. Line bottoms with buttered parchment paper and dust with flour.

Sift the flour, baking powder, soda, and salt into a medium bowl; whisk to combine evenly. Stir the sour cream, lemon juice and vanilla together in a liquid measuring cup, and set aside.

Beat the butter in a standing mixer with the paddle attachment on high until light and creamy, about 2 minutes. Stop and scrape butter off the sides of the bowl. Continue beating while gradually adding the sugar-- it should take a couple minutes to add all the sugar.

Continue beating until very light and fluffy, about 3 to 4 minutes more. Scrape down the sides of the bowl and beat in the lemon zest. Add the eggs, 1 at a time, beating well after each addition.

At low speed, add the flour mixture in 3 parts, alternating with the sour cream in 2 parts, beginning and ending with the flour. Scrape the sides of the bowl and mix for 15 seconds longer.

Divide the batter evenly between the prepared pans and smooth the top with a knife. (Lightly tap the pan on the counter so the batter settles evenly.)

Bake the cakes until a toothpick inserted in the center comes out clean, about 35 to 40 minutes. Cool in the pan on a rack for 20 minutes; then turn cakes out onto the rack to cool completely.

FOR THE ICING:
Bring a few inches of water to a boil in a saucepan that can hold a mixer's bowl above the water. Whisk the sugar, the egg whites, lemon juice, cream of tartar, and salt in the bowl by hand. Set the bowl above the boiling water and continue whisking until the mixture is hot to the touch and the sugar dissolves, about 1 to 2 minutes. Transfer the bowl to a standing mixer fitted with the whisk attachment and beat the whites at medium-high speed until they almost holds a stiff peak and are cool, about 10 minutes. Beat in the butter, a little at a time, until the icing is smooth and spreadable.

(If the icing separates, just keep beating and it will come back together.)

TO ASSEMBLE THE CAKE:
Slice each cake in half horizontally with a serrated knife, to make 4 even layers, taking care that they are as flat and straight as possible.

Set a large flat plate on a large inverted bowl or bottom of a salad spinner (of course, if you have a cake stand, use that), dabbing a little frosting on the bottom of the plate to secure it. Place a cake layer top side up on the plate.

Using an offset spatula spread about half of the jam in a thin layer over the first cake layer, leaving about 1/4-inch border along the outside. Lay the second cake layer on top, stacking it as straight as possible. Using an offset spatula spread about 1 cup of the icing on the top layer. Place a third cake layer on top. Spread remaining red raspberry jam over the cake layer and place the final layer on top, pressing down lightly to secure all 4 layers together. Spread about 3/4 of the remaining icing around the sides with a knife or offset spatula, then ice the top of the cake. Use an offset spatula to smooth icing as much as possible. Garnish with additional candied almonds and sprinkle the top of the cake with pastel colored sanding sugars.

Serve immediately or set aside at room temperature for up to 2 hours before serving. If refrigerating the cake, bring to room temperature 30 minutes before serving.

COOK'S NOTE:
Double wrap the cake in plastic wrap and store in the freezer for up to 2 months.

Yield: 8 to 10 servings
Copyright 2007 Television Food Network, G.P. All rights reserved