Choux Pastry: Preheat oven to 400 degrees F (205 degrees C) and place rack in center of oven. Line a baking sheet with parchment paper. 

In a bowl sift together the flour, sugar and salt. Set aside. 

Place the butter and water in a heavy saucepan over medium heat and bring to a boil. Remove from heat and, with a wooden spoon or spatula, quickly add the flour mixture. Return to heat and stir constantly until the dough comes away from the sides of the pan and forms a thick smooth ball (about a minute or two). Transfer the dough to your electric mixer, or with a hand mixer, and beat on low speed a minute or two to release the steam from the dough. Once the dough is lukewarm start adding the lightly beaten eggs and continue to mix until you have a smooth thick sticky paste. Spoon or pipe 12 mounds of dough onto the baking sheet, spacing them a couple of inches apart. Beat together the egg and salt for the glaze. With a pastry brush, gently brush the glaze on the tops of the dough. 

Bake for 15 minutes and then reduce the oven temperature to 350 degrees F (177 degrees C). Bake for a further 30 to 40 minutes or until the shells are a nice amber color and when split, are dry inside. Turn the oven off and, with the oven door slightly ajar, let the shells dry out for a further 10 - 15 minutes. Remove from oven and let cool on a wire rack. (The puffs can be frozen. Defrost the puffs and then reheat in a 350 degree F (177 degree C) oven for 5 to 10 minutes, or until crisp. Cool before filling with ice cream.)

Chocolate Ganache:  Place the chopped chocolate in a medium sized stainless steel bowl. Set aside. Heat the cream and butter in a small saucepan over medium heat. Bring just to a boil. Immediately pour the boiling cream over the chocolate and allow to stand for 5 minutes. Stir with a whisk until smooth. If desired, add the liqueur. Use immediately. (The ganache can be made ahead and stored in the refrigerator for up to a week. Reheat in a heatproof bowl set over a saucepan of simmering water.)

To Assemble: Split the pastry shells in half, fill the bottom halves of the shells with a scoop of vanilla ice cream, and replace the top. Drizzle each profiterole liberally with warm chocolate ganache. Serve immediately.

Note: Truffles can be made with leftover Ganache. Truffles are just small balls of chocolate that can be rolled into cocoa powder, powdered sugar or toasted chopped nuts.  Make sure the chocolate ganache is well chilled before forming into balls. You can use your hands to form the truffles, or else a melon baller or small spoon. Truffles can be refrigerated for a couple of weeks or else frozen for a couple of months.

Serves 6.