Preheat your oven to 410°F/210°C. Draw 1½ inches circles on parchment paper with some distance between each circle. Place this parchment paper drawn side down on a baking tray.

In a bowl whisk the eggs together. Set aside.

In a medium saucepan, bring water, butter, sugar, and salt to a boil over medium-high heat. Stir until the butter is melted. Switch off the heat and add flour all at once. Stir vigorously with a spatula until no flour is visible and the mixture forms a dough. Cook the dough on medium-low heat till the dough pulls away from the sides of the pan and forms a thin layer on the bottom of the pan, about 1-2 minutes.

Remove the saucepan from the heat and transfer the dough into a bowl. Let it cool down. Mix it with a whisk or electric whisker to release some steam.

Add the whisked eggs, in 3-4 parts, stirring or mixing with a mixer well after each addition until fully incorporated. When the spoon or whisk is lifted, with some dough and let it fall back into the bowl. It should slowly form a "V" shape and eventually break off. This is the perfect consistency of dough. You may not require three eggs for this or you may need more. So you should check the consistency after every addition of eggs.

Transfer the dough to a piping bag fitted with a large round tip. Pipe 1 1/2-inch mounds onto the prepared baking sheet, leaving some space between each puff to allow for expansion.

If peaks are formed during piping, wet your fingertip and smooth out the peaks. Dust with powdered sugar.

Place the baking sheet in the preheated oven and bake for 15 minutes. Then reduce the oven temperature to 350°F /180°C and continue baking for an additional 20-25 minutes, or until the puffs are golden brown and crisp.

Remove the puffs from the oven and let them cool completely on a wire rack.

In a medium saucepan, heat the milk and vanilla extract over medium heat until it reaches a simmer.

In a separate mixing bowl, whisk together the sugar, egg yolks, and cornstarch until smooth and pale in color.

Slowly pour the hot milk into the egg mixture, whisking constantly to temper the eggs. Once combined, pour the mixture back into the saucepan.

Cook the mixture over medium heat, whisking constantly, until it thickens and comes to a boil. This will take about 2-3 minutes. Remove from heat and stir in the chilled butter.

Transfer the pastry cream to a clean bowl to remove any lumps. Cover the surface of the cream with plastic wrap to prevent skin from forming. Chill in the refrigerator until completely cold.

In a bowl beat heavy/whipping cream with powdered sugar till thickened. Add the pastry cream and beat until a smooth consistency is achieved. Chill the pastry cream till further use.

Fill the pastry cream into a piping bag fitted with a small and narrow nozzle.

Fill each puff with pastry cream. You can either pierce the bottom of the puff with the nozzle and pipe in the cream. Or cut the puffs horizontally, pipe cream on the bottom part, and place the top part on top like a sandwich.

Serve the cream puffs immediately or refrigerate until ready to serve. Dust with powdered sugar before serving if desired.