Preheat oven to 425°F and set the rack on the middle level. Line 2 baking sheets with parchment paper or silpats.

Place the butter, sugar, water, and milk in a large saucepan. Turn the heat to medium and let the mixture come up to a boil.

Once boiling, add the flour and stir well until all of the flour is incorporated and the mixture comes together into a ball (about 2 minutes).

Remove the pan from the heat and stir the dough around with a spatula to cool it down. Wait at least 5 minutes before adding the eggs.

Add one lightly beaten egg and mix well until fully incorporated. Repeat for the remaining eggs, one at a time.

Place the dough into a piping bag with a circular tip. Pipe 1-inch tall by 2-inch wide mounds on the prepared baking sheets at least 2 inches apart. Flatten any pointy tops with a wet finger.

Bake for 10 minutes at 425°F, then lower the temperature to 325°F and bake for another 17-20 minutes or until golden. Remove from the oven and transfer to a wire rack to finish cooling after 10 minutes.

Prepare a large bowl filled with ice water for the pastry cream.

In a medium saucepan over low heat, warm the milk, cream, and vanilla.

In a separate pot (not on the stove), add the egg yolks, sugar, and cornstarch and whisk until combined. Gradually whisk in the warm milk and cream mixture.

Turn the heat to medium and continue whisking. Let the mixture come to a boil and thicken. Once it thoroughly coats the back of a wooden spoon, turn off the heat and mix in 1 tablespoon of butter.

Pour the pastry cream into a medium bowl and cover tightly with plastic wrap. Place the bowl into the ice water until cold. Remove from the ice water when cool.

Slice the pastry in half for easier filling or make a hole in each. Place the cooled pastry cream into a piping bag with a star tip. Fill the bottom of the pastry with cream and close it up like a sandwich.

Sprinkle with powdered sugar. Enjoy!