Chocolate Caramel Diamonds

Preparation

1. Make cake:

   Step 1

   Preheat oven to 375°F. Butter a 9-inch square baking pan and line bottom with wax paper.

   Step 2

   Chop chocolate into small pieces. In a double boiler or a metal bowl set over a saucepan of barely simmering water melt chocolate and butter, stirring until smooth. Remove top of double boiler or bowl from heat and whisk sugar into chocolate mixture. Whisk in eggs 1 at a time until combined well. Sift flour and cocoa powder over chocolate mixture and whisk until just combined. Pour batter into baking pan and bake in middle of oven until a tester comes out clean, about 20 minutes. Cool cake completely in pan on a rack and invert onto a baking sheet lined with wax paper.

2. Make ganache:

   Step 3

   Chop chocolate. In a dry heavy saucepan cook sugar over moderate heat, without stirring, until it begins to melt. Continue to cook sugar, stirring with a fork, until a deep-golden caramel. Remove pan from heat and add cream (mixture will bubble up and steam). Simmer mixture, stirring, until caramel is dissolved. Remove pan from heat and add chocolate, stirring until mixture is smooth. Pour ganache over top of cake and smooth with a spatula. Chill cake, uncovered, at least 30 minutes and, covered, up to 3 days.

3. Make topping:

   Step 4

   Lightly grease a baking sheet.

   Step 5

   In a dry small heavy saucepan cook sugar over moderately low heat, stirring slowly with a fork (to help sugar melt evenly), until a pale-golden caramel. Continue to cook caramel, without stirring, gently swirling pan, until golden. Remove pan from heat and pour caramel onto baking sheet. Cool caramel completely.

   Step 6

   Pry caramel from baking sheet with your fingers and in a food processor pulse caramel until coarsely ground. Sprinkle the ground caramel evenly over top of cake and with a sharp knife cut cake into 1 1/4-inch diamonds.