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.