Instructions: For Frosting:
Combine all ingredients in heavy large saucepan. Whisk over medium heat until chocolate melts and mixture is smooth and just begins to bubble, about 8 minutes. Refrigerate until just thick enough to spread, stirring occasionally, about 1 1/2 hours.

Meanwhile, prepare cake:
Preheat oven to 350 F. Line 15 1/2 x 10 1/2 x 1 inch baking sheet with foil, leaving overhang. Grease foil. Sift 1/2 cup sugar, cocoa powder, cake meal and potato starch into medium bowl.

Combine egg whites and salt in large bowl. Using handheld electric mixer, beat whites until soft peaks form. Gradually add 1/2 cup sugar; beat until stiff but not dry. Using same beaters, beat yolks and 1/2 cup sugar in another large bowl until thick, about 2 minutes. Gradually beat in oil, then nondairy creamer.

Add dry ingredients; beat just until blended. Fold whites into yolk mixture in 3 additions.

Spread batter in prepared pan. Bake until tester inserted into center comes out dry and cake feels firm to touch, about 20 minutes. Cool cake in pan on rack. Freeze cake just until firm, about 30 minutes.

Using foil as aid, lift cake onto work surface. Cut cake crosswise into 3 rectangles, each about 5 x 10 inches. Slide large spatula under 1 cake rectangle; transfer to platter. Spread 2/3 cup frosting over. Top with second layer. Spread 2/3 cup frosting over. Top with third layer. Spread very thin layer of frosting over top and sides of cake to coat thinly and anchor crumbs. Refrigerate 15 minutes to set thin coat of frosting. Spread remaining frosting decoratively over cake. Refrigerate until cold, about 4 hours. (Can be made 3 days ahead. Cover loosely with foil; keep refrigerated.)

Cover top of cake with chocolate shavings and garnish with mint, if desired.

Cut crosswise into slices and serve.

Serves 8 to 10.

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