Crust
1/2 C. graham cracker crumbs
1/2 C. finely chopped walnuts
1 C. finely chopped almonds
1/2 C. granulated sugar
1 stick (1/2 C.) unsalted butter, melted

Preheat oven to 350°F. and lightly oil a 9 1/2- by 2-inch springform pan.

In a bowl stir together crust ingredients until combined well and press onto bottom of pan. Bake crust in middle of oven 15 minutes, or until pale golden, and cool in pan on a rack.

Chocolate Layer
2 C. heavy cream
16 oz. semisweet chocolate, chopped coarse
2 T. light corn syrup
1 stick (1/2 C.) unsalted butter, cut into pieces

In a saucepan heat cream, chocolate, and corn syrup over moderately high heat, stirring occasionally, until chocolate is melted and mixture just comes to a boil. Remove pan from heat and stir in butter, one piece at a time, until smooth. Pour mixture over crust in pan and chill, until firm, about 3 hours.

Buttercream Layer
1 1/2 C. granulated sugar
1/2 C. water
6 large egg yolks
3 sticks (1 1/2 C.) unsalted butter, softened
1/2 C. Kahlúa
4 ounces semisweet chocolate,
    chopped, melted, and cooled

In a saucepan cook sugar and water over moderately high heat, stirring occasionally, until sugar is melted. Simmer syrup, undisturbed, until a candy thermometer registers 240°F.

In a bowl with an electric mixer beat yolks until smooth. Add hot syrup in a stream, beating on high speed until thickened and cooled. Reduce speed to medium and beat in butter, a little at a time. Beat in Kahlúa and chocolate until combined well. Spread buttercream over chocolate layer and chill until firm, about 3 hours.