Frozen Hazelnut-Tangerine Tiramisu

For Praline: Lightly oil baking sheet. Stir sugar and water in heavy medium saucepan over medium heat until sugar dissolves. Increase heat and boil without stirring until syrup turns deep amber, brushing down sides of pan with pastry brush dipped into water and swirling pan occasionally. Mix in nuts. Pour onto prepared sheet; cool. Coarsely chop praline. For Filling: Boil tangerine juice in heavy large saucepan until reduced to 1/4 cup, about 12 minutes. Set aside. Whisk 1 cup sugar and yolks in large metal bowl. Whisk in 1 cup water. Set bowl over saucepan of simmering water and whisk constantly until candy thermometer registers 180F., about 5 minutes. Remove from over water. Using electric mixer, beat mixture until cool, about 5 minutes. Mix in tangerine juice, cream and peel. Add mascarpone and 2 tablespoons Grand Marnier and beat until smooth. Fold in 1 cup praline (reserve remaining praline for another use). Chill filling while preparing biscuits. Line 9-inch-diameter springform pan with 2 3/4-inch-high sides with plastic wrap. Stir remaining 10 tablespoons sugar, 10 tablespoons water and espresso powder in heavy small saucepan over low heat until sugar dissolves. Mix in 5 tablespoons Grand Marnier. Cool syrup. Using sharp knife, trim 1 biscuit to 3-inch length. Soak biscuit in syrup 10 seconds per side. Place rounded end up and sugared side against side of prepared pan. Repeat with as many biscuits as necessary to cover sides of pan. Soak more biscuits in syrup and place on bottom of pan, covering completely. Pour half of filling into pan. Soak more biscuits in syrup 10 seconds per side; place atop filling, covering completely. Spoon remaining filling over. Freeze overnight. Release pan sides from cake. Fold down plastic. Sift cocoa over dessert. Garnish with tangerine slices, if desired. Serves 12. Bon Appetit January 1994