Preheat oven to 400°F and line a baking sheet with parchment paper.

In a saucepan, combine water, butter, and salt. Bring to a full boil so the butter is completely melted.

Add the flour all at once and immediately begin stirring. The mixture will look rough at first, then come together into a thick dough.

Continue cooking and stirring for 1 to 2 minutes until the dough forms a smooth ball and leaves a thin film on the bottom of the pan. This step removes excess moisture and helps the shells puff properly.

Transfer the dough to a mixing bowl and let cool for about 5 minutes until warm but not hot.

Add eggs one at a time, mixing fully after each addition. The dough may look separated at first but will come back together.

After all eggs are added, the dough should be smooth, glossy, and fall slowly from a spoon in a ribbon. It should hold its shape but not be stiff.

Bake for 20 minutes without opening the oven.

Reduce temperature to 350°F and bake another 10 to 15 minutes until deeply golden and dry.

In a saucepan, heat milk, vanilla, and sugar until steaming but not boiling. Set aside.

In a separate large saucepan, cook sugar over medium heat until melted and deep amber.

Reduce heat to low. Slowly add the warm milk mixture in small amounts while whisking constantly. Expect bubbling and steam. Continue until smooth.

In a bowl, whisk together whole eggs, egg yolks, sugar, and cornstarch until smooth.

Slowly add the hot caramel milk to the egg mixture while whisking constantly to temper.

Remove from heat and stir in salt.

Once chilled, whisk until smooth before using.

Transfer pastry cream to a piping bag.

Fill shells by either by slicing in half and filling or piping from the bottom

Fill until shells feel full but not overly heavy.

Dust with powdered sugar or drizzle with caramel or chocolate if desired.

Serve immediately for best texture or refrigerate until ready to serve.