02Whisk sugar, cocoa, and cornstarch in heavy medium saucepan. Gradually whisk in 1 cup half and half. Whisk in remaining 2 1/2 cups half and half and yolks. Whisk over medium-high heat until mixture thickens and boils, whisking constantly, about 12 minutes. Remove from heat. Add both chocolates and butter; whisk until melted and smooth. Mix in vanilla. Transfer filling to crust. Press plastic wrap directly onto surface of filling and chill until filling sets, at least 6 hours. (Can be made 2 days ahead. Keep chilled.)
03Beat all ingredients in large bowl until peaks form. (Can be made 1 day ahead. Cover and refrigerate. Rewhisk to thicken before serving, if necessary.)
04Peel plastic off pie. Cut pie into wedges. Spoon dollop of cream atop each slice. Garnish with chocolate-covered espresso beans and serve.