Caramel-Pecan Bûche de Noël

Preheat oven to 350°F. Line 17x12x1-inch rimmed baking sheet with parchment; butter paper. Pulse nuts and flour in processor until nuts are finely chopped (not ground). Using electric mixer, beat egg whites and salt in very large bowl until foamy. With mixer running, gradually beat in 1/4 cup sugar, beating just until stiff peaks form. Using electric mixer, beat yolks with 1/3 cup sugar and bourbon in large bowl until thickened, about 5 minutes. Add yolk mixture to egg-white mixture. Sprinkle nuts over; gently fold until almost incorporated. Add butter; fold gently just to blend. Pour into prepared baking sheet, spreading batter gently to form even layer.

Bake cake until edges begin to brown and cake is firm to touch, about 14 minutes. Cool in pan on rack.

Stir 1 1/4 cups sugar and 1/3 cup water in heavy medium saucepan over medium heat until sugar dissolves. Increase heat; boil without stirring until deep amber, occasionally swirling pan and brushing down sides with wet pastry brush, about 9 minutes (time will vary, depending on size of pan). Remove from heat; immediately add cream (mixture will bubble vigorously). Whisk in butter, bourbon, and salt. Stir over medium heat until any caramel bits dissolve. Transfer 1 cup caramel sauce to small pitcher. Add chocolate to remaining caramel in saucepan. Let stand off heat 5 minutes; whisk until smooth. Transfer to bowl. Let frosting stand until spreadable, stirring occasionally, about 1 hour.

Spread 1 cup frosting over cake in even layer. Beginning at 1 long side and using parchment as aid, roll up cake jelly-roll style. Starting 1 inch in from each end of cake, cut off 3-inch-long diagonal piece from each end. Arrange cake, seam side down, on platter. Spread cut side of each 3-inch cake piece with some of frosting. Attach 1 cake piece, frosting side down, to top of cake near 1 end. Attach second piece to side of cake near opposite end. Cover cake with remaining frosting. Run fork in concentric circles on cake ends. Do ahead Can be made 1 day ahead. Cover loosely with waxed paper and let stand at room temperature.

Garnish platter with leaves. Sprinkle cake lightly with powdered sugar. Cut cake into slices and serve with bananas, if desired, ice cream, and sauce.