In a medium saucepan, combine 1 cup water, ½ cup milk, ½ cup unsalted butter, 1 tablespoon sugar, and a pinch of salt. Bring this mixture to a rolling boil over medium heat.

Once boiling, quickly add 1 cup of all-purpose flour and stir vigorously with a wooden spoon until the dough forms a ball and pulls away from the sides of the pan, about 2 minutes.

Allow the choux dough to cool for about 5 minutes.

Once slightly cooled, beat in 4 room temperature eggs, one at a time, mixing well after each addition until the dough is smooth and glossy.

Preheat your oven to 400°F (200°C) and line two baking sheets with parchment paper. Using a piping bag fitted with a large round tip, pipe uniform rounds of choux dough onto the prepared sheets, about 2 inches apart.

Place the baking sheets in the preheated oven and bake for approximately 20 minutes. Avoid opening the oven door during this time to prevent the choux from collapsing.

After about 15-20 minutes, transfer the baked choux buns to a wire rack to cool completely.

In a bowl, whisk together 4 egg yolks, ½ cup sugar, and 2 tablespoons cornstarch. Gradually add 2 cups of hot milk, whisking continuously to combine.

Transfer this mixture to a saucepan and cook over medium heat, stirring until thickened, about 5 minutes. Remove from heat and stir in 2 tablespoons butter and ½ cup pistachio paste, then let chill.

Once your choux buns are completely cooled, use a small sharp knife to poke a hole in the base of each bun. Fill a piping bag with the chilled pistachio cream and gently squeeze it into each bun until you feel a slight heft.

To make the chocolate glaze, heat ½ cup of heavy cream until just simmering, then pour it over 4 ounces of chopped dark chocolate in a bowl. Let it sit for a few minutes and then stir until smooth.

Add in 1 tablespoon of butter for added shine and smoothness, creating a luscious glaze to crown your choux buns.

Dip the filled choux buns into the warm chocolate glaze to coat the tops beautifully. Consider adding a swirl of pistachio cream or sprinkle with chopped roasted pistachios before serving.