Remove from heat and quickly add the sifted flour all at once. Stir vigorously with a wooden spoon until a smooth dough forms and pulls away from the sides of the pan.

Transfer the dough to a mixing bowl and let it cool slightly for about 5 minutes.

With an electric mixer on medium speed, add the eggs one at a time, mixing well after each addition. The dough should be smooth and glossy.

Transfer the dough to a piping bag fitted with a large round tip. Pipe 1-inch mounds onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Bake the Profiteroles: Preheat oven to 400°F (200°C). Bake for 20-25 minutes, or until the profiteroles are golden brown and puffed up.

Turn off the oven and prop the door open slightly with a wooden spoon. Let the profiteroles cool in the oven for another 30 minutes.

Make the Cream Filling: While the profiteroles are cooling, in a mixing bowl, combine heavy cream, powdered sugar, and vanilla extract. Beat with an electric mixer until stiff peaks form.

Make the Chocolate Sauce: In a heatproof bowl set over a saucepan of simmering water (or in the microwave), combine chopped chocolate and heavy cream. Stir until smooth and melted.

Assemble the Profiteroles: Once the profiteroles are completely cool, use a small knife to make a slit in the side of each one. Fill with the whipped cream using a piping bag or spoon.

Serve: Drizzle with chocolate sauce and serve immediately.