1 cup toasted and ground mixed walnuts and pecans

Whipped cream:

1 cup water

1/2 teaspoon agar agar

3 cups non-homogenized heavy cream

1/2 cup confectioners' sugar

1 teaspoon vanilla

Buttercream:

1 pound (2 cups) unsalted butter, at room temperature (pliable, but not soft)

1/2 cup vegetable shortening

4 cups confectioners' sugar

2 teaspoons vanilla

2 1/2 tablespoons vegetable oil

1/4 cup Dutch-process cocoa powder

1 Heat the oven to 350 degrees. For the cake, grease two 9-inch baking pans; line with parchment paper circles. Beat 2 cups sugar and 3 eggs in a large bowl until fluffy and creamy, 3 minutes. Blend in 1 1/4 cups oil and 4 teaspoons vanilla; beat, 2 minutes.

2 Combine boiling water and 1/2 cup cocoa powder in a second bowl. Stir to dissolve; mix in baking soda and salt. Pour into batter; incorporate. Add flour; mix until blended and smooth. Pour into prepared pans and tap pans to release bubbles. Bake until the cake springs back when touched, 35-40 minutes. Remove from oven; let rest in pans, 5 minutes. Turn onto racks. Let cakes cool completely.

3 Meanwhile, make the whipped cream. Place 1 cup water in a saucepan with 1/2 teaspoon agar agar. Heat to a boil; cook at a boil, 4 1/2 minutes. Let solution cool just until you can immerse your finger in it — still quite warm and liquid — this takes about 3 to 3 1/2 minutes. Meanwhile, combine 3 cups of cream with 1/2 cup powdered sugar and 1 teaspoon vanilla. Turn mixer to low speed. Before cream reaches soft peak stage, add 3 tablespoons of the warm liquid agar/water solution to cream all at once. Whip until consistency firms up. Note: The whipped cream will not be super firm--just firmer than typical whipped cream.

4 Make the light chocolate buttercream. Whip two cups of room temperature unsalted butter with 1/2 cup vegetable shortening and 4 cups powdered sugar at low speed for 8 to 10 minutes until the mixture is fluffy. Add two teaspoons vanilla. Whip again just to incorporate. Mix together 2 1/2 tablespoon oil with 4 tablespoons Dutch-process cocoa powder. Whisk into buttercream until evenly distributed.

5 Assemble cake. Trim the "dome" off the top of each fudge layer to ensure each cake layer is exactly level and of the same thickness. Place first fudge layer on a cake liner on a footed cake stand. Carefully pipe 1-inch of buttercream around the rim of the fudge layer, so you now have a standing lip of buttercream on the cake layer. Fill this with 1-inch tall whipped cream. Add several more spoons of whipped cream onto the center. Layer the second fudge layer of cake over the whipped cream layer. Using an offset spatula, carefully seal the outside edge of the cake (sealing whipped cream in) with buttercream, using a little more buttercream if needed. Frost top of cake with buttercream. Frost sides of cake with buttercream. Apply crushed nuts (toasted walnut and pecan) to sides of the cake.

6 Freeze the cake, which will ensure that the whipped cream layer and buttercream will firm up. Set cake out 30 to 45 minutes before serving to soften.

Do you have a question about food or drink? E-mail Bill Daley at: wdaley@tribune.com. Snail mail inquiries should be sent to: Bill Daley, Chicago Tribune, 435 N. Michigan Ave., Chicago 60611. Twitter @billdaley.