1. Place a wire rack in a large rimmed pan; set aside. For ganache, place white chocolate in a medium-size heat-proof glass medium bowl. In a small saucepan bring cream and orange zest and juice just to boiling over medium-high heat; remove from heat. Pour hot cream mixture through a fine-mesh sieve over white chocolate in bowl. Discard zest. Stir until white chocolate is melted and ganache is smooth. Cool 15 minutes.
2. Meanwhile, for petits fours, trim brown crust from bottom, top and sides of frozen cake to form a rectangle with even edges. (Discard or reserve cake trimmings for another use.) Cut cake rectangle lengthwise in half, then cut 10 (1½‑inch) squares. Cut each square in half, creating a top and bottom for each petit four.
3. Stir marmalade until smooth. Spread about ½ teaspoon on a cake slice. Place a second cake slice on top, smoothing away any excess marmalade. Repeat for remaining 9 petits fours.
4. Place petits fours on wire rack in baking pan. Spoon ganache over each top and sides. Let stand 1 to 2 hours or until ganache is set. Garnish petits fours with fondant flowers.

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*Note: For tools to make fondant flowers, purchase Wilton’s How to Decorate with Fondant Shapes and Cut‑Outs Kit, item #2116-3007, available at most craft stores.