Italian Gianduia Loaf with Custard Sauce

Preparation

1. For Filling:

   Step 1

   Line 5 1/2- to 6-cup metal loaf pan with plastic wrap, overlapping sides. Melt chocolate and butter with corn syrup in heavy large saucepan over medium-low heat, stirring until smooth. Cool to lukewarm, whisking occasionally.

   Step 2

   Whisk 1/4 cup cream, 4 tablespoons Frangelico, yolks, sugar and 2 tablespoons water in small metal bowl. Set bowl over saucepan of simmering water and whisk constantly until candy thermometer registers 160°F., about 3 minutes. Remove from over water. Add yolk mixture and remaining 2 tablespoons Frangelico to chocolate mixture in pan; whisk until smooth. Mix in nuts. Chill until cool, about 10 minutes. Using electric mixer, beat remaining 1/4 cup cream with sour cream in large bowl to stiff peaks. Add chocolate mixture and fold together. Pour filling into prepared pan; smooth top. Cover and chill overnight.

2. For Glaze:

   Step 3

   Combine all ingredients in heavy medium saucepan. Stir over low heat until melted. Cool to lukewarm. Pour 1/2 cup glaze over filling in pan; shake pan gently to smooth top. Freeze until glaze sets, about 20 minutes.

   Step 4

   Line cookie sheet with foil. Lift loaf from pan. Turn loaf out onto foil; peel off plastic. Whisk remaining glaze over low heat until just spreadable. Pour all but 1/4 cup glaze over loaf. Spread over top and sides with icing spatula, spreading glaze that runs onto foil up sides of loaf to cover completely. Chill 1 hour. (Can be prepared 2 days ahead. Cover and chill loaf and reserved 1/4 cup glaze separately.)

3. For Sauce:

   Step 5

   Bring half and half to simmer in heavy medium saucepan. Scrape in seeds from vanilla bean; add bean. Whisk yolks and sugar in medium bowl to blend. Whisk in hot half and half mixture. Return mixture to saucepan and stir over medium-low heat until custard thickens and leaves path on back of spoon when finger is drawn across, about 5 minutes; do not boil. Strain into bowl. Mix in cream and Frangelico. Cover and chill until cold. (Can be prepared 2 days ahead.)

   Step 6

   Melt milk chocolate in top of double boiler over simmering water, stirring until smooth. Spoon all but 2 tablespoons melted chocolate into parchment cone. Remove loaf from foil and transfer to platter. Pipe chocolate lines crosswise atop loaf, spacing 1/8 inch apart. Dip 1 hazelnut halfway into chocolate in pan; place atop center of loaf. Repeat with remaining nuts, spacing evenly and forming line down center. (Can be prepared 3 days ahead; refrigerate.)

   Step 7

   Using long thin knife, cut loaf into 1/2-inch-thick slices, wiping knife clean between cuts. Place slices on plate; surround with sauce. Whisk reserved glaze over low heat until melted. Spoon into parchment cone. Pipe Zs atop sauce.