Chocolate Orange Jubilee Cake

1 pkg. devil's food cake mix
3 eggs
2/3 cup orange juice
2/3 cup water
1/3 cup vegetable oil
1 Tbls. grated orange zest
1 1/2 cups butter, softened
2 Tbls. orange juice
1 Tbls. grated orange zest
4 cups confectioner's sugar, sifted
2 egg yolks
Chocolate curls or shaved chocolate
Orange slices, candied or fresh

Preheat oven to 350 degrees. F.

CAKE:
In a large mixer bowl, combine cake mix, eggs, orange juice, water, oil, and zest. Beat on medium speed for 2 minutes. Spread batter in three prepared 8-inch or 9-inch round cake pans, dividing evenly. Bake 20 to 30 minutes. Cool 10 minutes in pans on a wire rack then remove layers and cool completely. With a long, sharp knife, cut each layer horizontally in half to make 6 layers.

FILLING and FROSTING:
In a large mixer bowl, beat butter, orange juice and zest on medium speed until creamy. Gradually add confectioner's sugar and egg yolks, beating until smooth and fluffy.

ASSEMBLY:
Spread buttercream between each layer, placing one on top of the other on a a serving plate. Frost sides and top of cake, reserving for decoration. Decorate top of cake with rosettes of buttercream, chocolate curls, and orange slices.

Chill until serving. If using fresh orange slices, place on cake just before serving.