Preheat the oven to 425 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 the bowl of an electric mixer. Beat the dough on medium speeds and add the eggs, one at a time. Continue beating until the dough holds together. Remove the dough from the mixer and cool. Place the dough in a pastry bag fitted with a round tip and pipe out logs, 2 inches long, onto the lined baking sheet, about 2 inches apart. Place the pan in the oven and bake for 10 minutes. Reduce the heat to 375 degrees F. and continue to cook for 25 minutes. Do not remove the sheet from the oven until they are firm to the touch. Cool the shells completely. Fill a pastry bag, fitted with a small round tip, with the pastry cream. Place the eclairs on a wire rack underlined with a baking sheet. Spoon some of the glaze over each eclair. Refrigerate the eclairs until the glaze is set. Remove from the refrigerator and serve.
In a small mixing bowl, combine the cocoa powder, powdered sugar and milk. Mix until smooth.