In a medium saucepan, combine whole milk and ¼ cup (50g) of sugar. Heat over medium setting until steam rises and tiny bubbles form around the edges (do not boil).

In a heatproof bowl, whisk the egg yolks, remaining ¼ cup sugar, cornstarch, and salt together until pale and smooth.

Slowly drizzle roughly ½ cup of the hot milk into the egg yolk mixture while whisking constantly. This tempers the eggs so they do not curdle.

Pour the tempered egg mixture back into the saucepan with the remaining hot milk.

Cook over medium heat, whisking constantly and vigorously, until the mixture thickens into a glossy pudding-like consistency (about 2 minutes after reaching a boil).

Remove from heat immediately. Stir in the softened butter and vanilla paste until fully melted and integrated.

Press a sheet of plastic wrap directly onto the surface of the custard to prevent a skin from forming. Refrigerate for at least 2 hours until chilled and set.

Preheat your oven to 400°F (200°C). Line two large rimmed baking sheets with parchment paper.

In a heavy-bottomed medium saucepan, combine the water, whole milk, cubed butter, sugar, and salt. Bring to a rolling boil over medium-high heat.

As soon as the liquid boils, remove the pan from heat and add all the sifted all-purpose flour at once.

Stir vigorously with a sturdy wooden spoon or heat-resistant spatula until the flour absorbs the liquid and forms a thick, cohesive dough ball.

Return the saucepan to medium heat. Cook the dough for 1 to 2 minutes, mashing and stirring constantly against the sides and bottom of the pan. The dough is ready when a thin film coats the bottom of the pan and steam subsides slightly.

Transfer the hot dough into a large glass bowl (or the bowl of a stand mixer fitted with the paddle attachment). Let cool for 3 to 5 minutes so the heat doesn’t scramble the eggs.

Beat the dough on low speed (or stir vigorously by hand) for 1 minute to release excess steam.

Add the room temperature eggs one at a time, mixing thoroughly after each addition until fully incorporated before adding the next. The dough will look broken initially, but will smooth out.

Test the dough consistency: lift your spatula out of the bowl. The dough should fall slowly and leave a smooth, glossy ‘V’ shape hanging off the end of the spatula. If it feels too stiff, whisk your 5th reserved egg and add half of it.

Transfer the choux paste into a large piping bag fitted with a large round tip (1/2-inch size).

Pipe 2-inch mounds onto the prepared baking sheets, spacing them about 2 inches apart.

Wet your fingertip with water and gently smooth down any sharp peaks on top of the mounds to prevent burning.

Beat the remaining egg with 1 teaspoon of water and brush lightly over each mound.

Bake at 400°F (200°C) for 15 minutes without opening the oven door.

Lower oven temperature to 350°F (175°C) and bake for an additional 15 to 20 minutes until the shells are deep golden brown, firm, and sound hollow when tapped.

Turn off the oven, crack the oven door open slightly with a wooden spoon, and let the puffs rest inside for 10 minutes to release internal steam.

Remove the pastry shells from the oven and use a small toothpick or skewer to poke a tiny hole in the bottom of each puff to let trapped steam escape. Let cool completely on a wire rack.

Remove the chilled pastry cream from the fridge and whisk until smooth. (Optional: whip ½ cup cold heavy cream to stiff peaks and fold into the pastry cream for a lighter Diplomat cream).

Assembly Method A: Slice the top third off each cooled puff, pipe or spoon cream into the hollow bottom, and place the lid back on top.

Assembly Method B: Fitted a piping bag with a narrow filling tip, insert into the bottom hole, and pipe filling until the puff feels heavy.

Dust liberally with sifted powdered sugar right before serving.