Pastry Cream:

Line a quarter-sheet tray with a silicone mat. Set aside.

Add the milk to a saucepan and whisk in half of the sugar. Warm over medium heat until steaming. (Do not boil).

Meanwhile, whisk together egg yolks, flour, cornflour, vanilla bean paste, and remaining sugar in a medium bowl.

Gradually pour the hot milk into the egg mixture in a thin stream, whisking well after each addition. Do not to pour too quickly or add all of the milk at once.

Pour the mixture back into the saucepan. Cook over medium-low heat, stirring continuously with a whisk or spatula. Mixture will thicken as it cooks.

Bring thickened pastry cream to a low boil. Boil for 1-2 minutes, stirring continuously.

Pour pastry cream onto prepared tray, and use a rubber spatula to spread.

Wait until the pastry cream stops steaming, then cover with a sheet of clingfilm/plastic wrap, and use your hands to pat it down so that the plastic directly touches the pastry cream. (This prevents a rubbery “skin” from forming on top.)

Cool to room temperature, then refrigerate tray while you prepare the choux pastry.

Choux Pastry:

Preheat oven to 350° F / 176° C. Generously grease a half-sheet rimmed baking tray with butter.

In a medium saucepan, combine water, milk, butter, salt, and sugar. Bring to a boil.

Remove from heat and stir in the flour.

Return to medium heat and cook until the mixture clumps together and pulls away from the sides of the pan, about 30 seconds.

Tip mixture into a large bowl. With a rubber spatula, spread the pastry up the sides of the bowl. (This promotes faster cooling.)

Once cool, add the beaten egg in small portions, using a rubber spatula to incorporate. (The mixture will seem clumpy at first, then pasty, before forming soft, but not overly sticky, dough.) Continue adding egg, a small amount at a time, until the pastry drops easily from the spatula, making a “plopping” sound. You might have a small amount of beaten egg left over.

With a rubber spatula, scoop choux pastry into a large disposable piping bag fitted with a 1/2-inch round tip. On prepared tray, pipe 1 1/2-inch dots of choux pastry, about 1 inch apart.

With a pastry brush, egg wash the top of each dot.

Bake in preheated oven for 10 minutes. Reduce heat to 165° C / 330° F and bake for 25-30 minutes more, or until choux buns are crisp and deeply golden brown.

Transfer choux buns to a wire rack. (They should lift easily from the tray.) Allow to cool.

 Assembly and Decoration:

Scoop refrigerated pastry cream into a medium bowl. With a wire whisk, “knock back” the cream by whisking vigorously until it is smooth and creamy.

Scoop pastry cream into a piping bag fitted with 1/4-inch round tip.

With a wooden skewer, metal cake tester, or sharp paring knife, poke a hole in the bottom of each choux bun.

Insert piping tip into the hole and fill the bun with pastry cream.

Use the flat side of a knife to scrape away any excess pastry cream.

Sit buns on a wire rack. Place rack over a sheet of parchment or a parchment-lined tray.

Caramel Glaze:

In a small saucepan, stir together sugar, water, glucose, and sea salt, if using.

 

Bring to a boil, brushing down the sides of the pan with a damp pastry brush as needed.

Cook the caramel over medium heat until the mixture resembles honey, about 10 minutes. Do not stir the caramel. If necessary, you can swirl the pan occasionally to keep the caramel moving.

Remove from heat. Tilt the pan. Working quickly but carefully, dip the very top of each bun in the caramel. Sprinkle with crushed pistachios.

Allow choux buns to sit until caramel cools. Serve immediately.