Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper and set aside.
Make the choux dough: in a medium saucepan combine the Water, Whole Milk, Unsalted Butter, Granulated Sugar and Salt. Bring just to a boil over medium heat, stirring so the butter melts.
Remove the pan from the heat and add the All-Purpose Flour all at once. Stir vigorously with a wooden spoon until the mixture forms a smooth ball and pulls away from the sides of the pan. Return to low heat for 30–60 seconds while stirring to dry the dough slightly.
Transfer the dough to a bowl (or the bowl of a stand mixer) and let it cool for a few minutes. Beat in the Eggs one at a time, fully incorporating each before adding the next, until the dough is smooth, glossy and holds a peak that flops over slightly.
Pipe or spoon small mounds (about 1 to 1 1/2 inches in diameter) onto the prepared baking sheet, spacing them a few inches apart. Lightly wet your finger and smooth any peaks.
Bake at 425°F (220°C) for 10 minutes, then reduce the oven temperature to 350°F (175°C) and bake until the puffs are deep golden and dry inside, about 15–20 more minutes. Do not open the oven while they puff. When done, remove to a wire rack to cool and, if desired, slice the tops off to allow steam to escape.
Fill the puffs: let the Vanilla Ice Cream soften slightly so it’s scoopable, then spoon or pipe the ice cream into the cooled profiterole shells. Return filled profiteroles to the freezer for a short time if you want them very firm before finishing.
Make the chocolate sauce: chop the Dark Chocolate (60–70% Cocoa). Heat the Heavy Cream until it just begins to simmer, then pour it over the chopped chocolate and let sit for a minute. Stir until smooth and glossy, then whisk in a small piece of unsalted butter to enrich and shine the sauce.
To serve, arrange the filled profiteroles on a platter and drizzle with the warm chocolate sauce. Serve immediately so the contrast between crisp pastry, cold ice cream and warm chocolate is at its best.
