1-1/2 cups (375 mL) graham wafer crumbs
1/3 cup (75 mL) butter, melted
2 oz (57 g) semisweet chocolate, melted
4 egg yolks
1/2 cup (125 mL) granulated sugar
1/3 cup (75 mL) cornstarch
3 cups (750 mL) milk
2 tbsp (25 mL) butter
1 tsp (5 mL) vanilla
2 small bananas, sliced
1 cup (250 mL) whipping cream
2 tbsp (25 mL) semisweet chocolate, grated
Filling: In bowl, whisk together egg yolks, sugar, cornstarch and 1/2 cup (125 mL) of the milk; set aside.
In heavy saucepan, heat remaining milk over medium heat until bubbles form around edge; whisk into yolk mixture. Return to pan and cook over medium-low heat, stirring, until thick enough to mound on spoon, about 5 minutes. Stir in butter and vanilla. Scrape into bowl. Place plastic wrap directly on surface; refrigerate just until cooled, about 2 hours.
In bowl, stir graham wafer crumbs with butter until moistened; press onto bottom and up side of 9-inch (23 cm) pie plate. Refrigerate until firm, about 30 minutes.
Drizzle melted chocolate over bottom of crust; spread evenly with back of spoon. Refrigerate until set, about 10 minutes. Without stirring custard, spoon half over chocolate. Arrange banana slices over top, overlapping slightly. Top with remaining custard. Place plastic wrap directly on surface; refrigerate until cold, about 2 hours. (Make-ahead: Refrigerate for up to 12 hours.)
Garnish: In bowl, whip cream. Using piping bag or with spatula, pipe into rosettes or spread to cover top. Sprinkle with grated chocolate. (Make-ahead: Insert 6 toothpicks into pie; drape plastic wrap loosely over top and refrigerate for up to 4 hours.)