Hazelnut Crunch Cake with Honeyed Kumquats

Preparation

1. For nut crunch:

   Step 1

   Line baking sheet with foil. Stir sugar and 1/4 cup water in heavy medium saucepan over medium–low heat until sugar dissolves. Increase heat; boil without stirring until syrup turns deep amber, brushing down sides with wet pastry brush and swirling pan occasionally. Mix in nuts. Pour onto foil; cool completely. Coarsely chop nut crunch. Set aside.

2. For kumquats:

   Step 2

   Starting at rounded end, cut cross into each kumquat to within 1/4 inch of stem end. Bring wine, sugar, honey, and star anise to boil in heavy large saucepan, stirring until sugar dissolves. Scrape in seeds from vanilla bean; add bean. Add kumquats; simmer until almost tender, about 8 minutes. Using slotted spoon, transfer kumquats to plate; cool. Seed and finely chop enough kumquats to measure 2/3 cup (reserve remaining kumquats). Gently boil kumquat syrup until reduced to 11/4 cups, about 12 minutes. Cool.

3. For cake:

   Step 3

   Preheat oven to 350°F. Line 15 1/2 x 10 1/2 x 1–inch or 17 x 11 x 3/4–inch baking sheet with foil; butter and flour foil. Finely grind nuts with flour in processor; transfer to medium bowl. Whisk in baking powder, spice, and salt. Using electric mixer, beat butter and sugar in large bowl until well blended. Beat in yolks and extracts. Beat in dry ingredients alternately with milk in several additions, just until combined. Using clean dry beaters, beat whites in another large bowl until stiff but not dry. Fold 1/3 of whites into batter to lighten, then fold in remaining whites. Spread batter evenly in prepared pan.

   Step 4

   Bake cake until tester inserted into center comes out clean, about 20 minutes for 17 x 11–inch cake and 28 minutes for 15 1/2 x 10 1/2–inch cake. Cool cake in pan on rack 20 minutes. Run knife around cake to loosen. Turn cake out onto foil–lined rack; cool completely. Cut hazelnut cake crosswise into 3 equal pieces.

4. For frosting:

   Step 5

   Combine all ingredients in large bowl; beat to soft peaks (do not overbeat or mixture will curdle).

   Step 6

   Place 1 cake piece on platter. Spread 3/4 cup frosting over; sprinkle with 1/3 cup chopped kumquats and 1/3 cup nut crunch, then drizzle with 2 tablespoons kumquat syrup. Top with second cake piece. Spread 3/4 cup frosting over; sprinkle with 1/3 cup chopped kumquats and 1/3 cup nut crunch, then drizzle with 2 tablespoons kumquat syrup. Top with third cake piece. Spread remaining frosting over top and sides of cake. Drain remaining kumquats; remove seeds and any attached pulp. Top cake with kumquats, arranging like flowers. Do ahead Can be made 1 day ahead; cover and chill cake. Store remaining nut crunch and kumquat syrup at room temperature. Press remaining nut crunch around sides of cake. Drizzle 2 tablespoons syrup over cake and serve.