PREHEAT oven to 400° F. Line 2 baking sheets with parchment paper.
PLACE water, butter, sugar and salt in a large heavy-duty saucepan. Cook over medium-high heat, stirring frequently, until gently boiling and butter is melted. Add flour all at once; continue to stir until flour is incorporated and dough comes together and pulls away from the side of the pan. Remove from heat; scrape dough into bowl of stand mixer or large mixing bowl.
BEAT dough on medium speed for about 1 minute to help it cool down. Add the eggs one at a time, stopping to scrape down the side of the bowl periodically. Beat until dough is smooth, thick and glossy.
SPOON dough into a pastry bag fitted with a large plain round tip. Push the dough to the bottom of the bag using your hands or a bench scraper. Twist the top of the bag to seal.
PIPE dough into golf-ball size mounds on prepared baking sheets, about 2 inches apart. Keep mounds as high and round as possible. With a wet finger, lightly press down the swirl at the top of each puff.
BAKE for 10 minutes. Reduce oven temperature to 350Â° F; bake for an additional 15 minutes or until golden brown and fairly firm. Do not open the oven door while they are baking. Remove from oven; cool completely on baking sheets before filling.
HEAT cream in small saucepan over medium heat until just boiling. Add chocolate, butter and vanilla extract. Remove from heat; stir until chocolate is melted and sauce is smooth.
SLICE pastry puffs in half crosswise using a serrated knife. Fill each puff with a scoop of ice cream. Replace the tops and drizzle with chocolate sauce. Serve immediately.