Prepare the Choux Pastry: In a medium saucepan, combine the 80g of butter and 200ml of water. Place over medium heat and bring to a rolling boil, ensuring the butter is fully melted.

Remove the saucepan from the heat. Immediately add the 130g of all-purpose flour all at once. Stir vigorously with a wooden spoon or heat-resistant spatula until the mixture comes together to form a smooth ball of dough that pulls away from the sides of the pan.

Return the saucepan to low heat and continue to cook the dough, stirring constantly, for about 1-2 minutes. This helps to dry out the dough, which is essential for proper puffing. A thin film should form on the bottom of the pan. Remove from heat and transfer the dough to a large mixing bowl. Let it cool for 5-10 minutes until it's warm but not hot to the touch (you should be able to comfortably touch it). This prevents the eggs from scrambling.

Incorporate the Eggs: Gradually add the 3 eggs, one at a time, to the cooled dough, mixing thoroughly after each addition. You can use a wooden spoon, a hand mixer, or a stand mixer with a paddle attachment. Ensure each egg is fully incorporated and the dough is smooth before adding the next. The dough will look curdled and slippery at first, but it will come together. The final dough should be smooth, glossy, and thick enough to hold its shape but soft enough to pipe (it should form a "V" shape when lifted with a spoon).

Pipe the Choux Pastry: Preheat your oven to 170°C (340°F). Line a baking sheet with parchment paper. Transfer the choux pastry dough into a piping bag fitted with a large round tip (or a star tip for decorative puffs). Pipe 1.5 to 2-inch (3-5 cm) mounds of dough onto the prepared baking sheet, leaving about 2 inches between them as they will expand.

Smooth with Water: If desired, wet your finger with a little water and gently smooth down any peaks on top of the piped dough. This helps prevent them from burning.

Bake the Choux Puffs: Bake in the preheated oven at 170°C (340°F) for 40 minutes. Do not open the oven door during baking, especially for the first 25-30 minutes, as the puffs will collapse. The puffs should be golden brown, firm, and feel very light when picked up. If they feel heavy or soft, they might not be cooked through and could collapse upon cooling.

Once baked, turn off the oven, crack the door open slightly (you can wedge a wooden spoon in it), and let the puffs cool inside the oven for 15-20 minutes. This slow cooling helps them dry out completely and prevents them from deflating. Transfer them to a wire rack to cool completely before filling.

Prepare the Pastry Cream: While the choux puffs are cooling, prepare the pastry cream. In a medium bowl, whisk together the 2 egg yolks, 3 tablespoons of sugar, and 2 tablespoons of cornstarch until smooth and pale.

In a separate saucepan, heat the 200ml of whole milk over medium heat until it just begins to simmer around the edges (do not boil).

Gradually pour about half of the hot milk into the egg yolk mixture while whisking constantly. This tempers the yolks and prevents them from scrambling.

Pour the tempered egg yolk mixture back into the saucepan with the remaining hot milk. Cook over medium heat, whisking constantly and vigorously, until the custard thickens significantly and comes to a boil. Boil for 1 minute while whisking to ensure the cornstarch is fully cooked.

Remove from heat. If you want a perfectly smooth cream, press it through a fine-mesh sieve into a clean bowl. Cover the surface of the custard directly with plastic wrap to prevent a skin from forming. Place in the freezer (or refrigerator) until completely cooled, about 1-2 hours in the freezer or 3-4 hours in the refrigerator.

Prepare the Whipped Cream: Once the pastry cream is chilled, make the whipped cream. In a cold bowl (chilled in the freezer for 10-15 minutes), combine the 2/3 cup of cold heavy cream and 2 tablespoons of sugar. Beat with an electric mixer on medium-high speed until firm peaks form. Be careful not to overbeat, or it will turn grainy.

Assemble the Cream Puffs: Gently fold the chilled pastry cream into the whipped cream until just combined, or use them as separate fillings. Cut each cooled choux puff horizontally in half, or make a small hole in the bottom.

Fill the bottom half of each choux puff with the cream mixture using a spoon or piping bag. Place the top half back on.

Dust with powdered sugar, if desired, before serving.