Chocolate Pudding Souffle Cake

Preheat oven to 375 degrees. Grease a 9 inch springform pan. Melt
together butter and unsweetened chocolate in top of double boiler
over simmering, not boiling water, stirring until smooth. Set aside.
Mix together flour, baking powder and salt in small bowl. Separate 3
eggs, placing yolks in large bowl; reserve whites. Add 3 whole eggs
and 3/4 cup sugar to yolks; beat at high speed until pale and
lemon-colored, 2-3 minutes. Beat in chocolate mixture at low speed;
beat in flour mixture just until blended. Using clean beaters and a
clean medium-size bowl, beat egg whites until frothy. Add cream of
tartar and beat until soft peaks form. Beat in the remaining 1/4 cup
sugar until stiff, but not dry, peaks form. Stir about one-third of
whites into chocolate mixture until blended. Fold in the remaining
whites. Scrape into the prepared pan, smoothing top. Bake in
preheated oven 40 to 50 minutes or until cake is set in center.
Transfer pan to a rack to cool completetly. Refrigerate until firm.
Meanwhile, prepare pudding; Whisk together sugar and cornstarch in
medium-size heavy saucepan. Whisk in the cream. Bring to simmering
over medium-low heat, stirring constantly. Gradually whisk some of
the cream mixture into egg yolks. Scrape yolk mixture back into
saucepan. Cook over very low heat, whisking constantly, until pudding
is very thick, about 5 minutes; do not let boil. Remove saucepan from
heat. Stir in the chocolate and vanilla until melted and smooth.
Scrape the pudding into a bowl; place plastic wrap directly on the
surface. Refrigerate until cold and thickened for at least 2 hours.
To assemble: Remove sides of pan from cake. Using a serrated knife,
cut cake horizontally into 3 equal layers. Place 1 layer on serving
plate; spread top with 3/4 cup of pudding. Repeat with remaining cake
layers and pudding. Cover sides with pudding. Refrigerate cake; until
pudding is set.