Preheat the oven to 400 degrees F. In a saucepan, over high heat, whisk the butter and milk together, until all the butter has melted. Bring the liquid up to a boil. Whisk in the sugar. Combine the flour, baking powder and salt. Slowly stir in the flour mixture and continue to stir until the mixture forms a ball and pulls away from the sides of the pan. Remove from the heat and turn into a bowl, of an electric mixer. Beat the dough on medium speed and add the eggs, 1 at a time. Continue beating until the dough no longer looks slippery. Remove the dough from the mixer and cool. Place the dough in a pastry bag fitted with a round tip and pipe out 3-inch logs onto a parchment lined baking sheet, about 2 inches apart or use a large spoon and spoon them onto the baking sheet. Place the pan in the oven and bake for 10 minutes. Reduce the heat to 350 degrees F. and continue to cook for 25 minutes. Do not remove the sheet from the oven until the rounds are firm to the touch. Cool the shells before filling. Place the pastry cream in a pastry bag, fitted with a round tip, and fill each shell with the filling. Dip the top of each eclair in the chocolate. Set aside until the topping as set. Place the eclairs on a platter. Garnish with confectioners' sugar

In a mixing bowl, combine the egg yolks, cornstarch, and 1 cup of the heavy cream. Whisk to blend well. Set aside. Combine the remaining 1 1/2 cups cream and sugar in a large heavy-bottomed saucepan over medium heat. Whisk to dissolve the sugar and bring to a gentle boil, about 10 minutes. Slowly add the egg yolk mixture, whisking constantly and cook until it thickens, about 5 minutes. Be forewarned: the mixture will break. Don't be alarmed. Pour it into a glass bowl. Press a piece of plastic wrap down over the surface of the mixture to prevent a skin from forming. Let cool completely at room temperature. When cooled pour the mixture into the bowl of an electric mixer fitted with a wire whip. Beat at a medium speed to combine the mixture. If it will not combine, warm another 1/2 cup heavy cream and slowly add it to the mixture. Whip until you have a thick and creamy custard. Yield: about 2 cups