For the spicy chocolate pastry cream:
2 cups whole milk
4 large egg yolks
5 tablespoons granulated sugar
3 tablespoons cornstarch
2 teaspoons cinnamon
1 1/2 teaspoon chipotle powder
1 teaspoon red pepper flakes
6 ounces bittersweet chocolate (about 60%), finely chopped
1 ounce cocoa powder, preferably dutch process
2 tablespoons butter
For the choux:
1/2 cup whole milk
1/2 cup water
8 tablespoons unsalted butter
1 tablespoon granulated sugar
1/2 teaspoon salt
1 cup all-purpose flour
4 eggs, at room temperature
For finishing the eclairs:
4 tablespoons butter, melted
1/2 cup cinnamon sugar (1/2 cup sugar and 1 1/2 teaspoons cinnamon)
The pastry cream and choux dough are both adapted from the wonderful Dorie Greenspan.
For the pastry cream:
In a microwave or small saucepan, heat the 2 cups milk until hot. Set aside.
In a small bowl in the microwave, heat the chopped chocolate and cocoa powder, stirring at 30-second intervals. You can also use a double boiler. When the chocolate is completely melted and smooth, set aside.
In a medium saucepan, whisk together egg yolks, cornstarch, sugar, salt, cinnamon, chipotle, and red pepper flakes. Add about 1/2 cup hot milk to the mixture and whisk thoroughly to temper the egg yolks so that they do not scramble. When the mixture is smooth, add the rest of the milk. Heat over medium heat, whisking continuously, until the mixture thickens and starts to bubble, then allow it to bubble for one or two minutes longer. Remove from the heat.
Whisk melted chocolate into the cooked pastry cream until they are completely combined. Add the butter and whisk until it is completely melted. Transfer the pastry cream to a medium bowl and press plastic wrap directly onto the surface of the cream to keep a skin from developing. Refrigerate until needed.
For the eclairs:
Preheat the oven to 425. Line 2 baking sheets with silicone liners or parchment paper.
In a medium saucepan, heat milk, water, 8 tablespoons of butter, 1 tablespoon of sugar, and salt on high heat until the butter is completely melted and the mixture comes to a boil. Lower the heat to medium and add the flour all at once. Stir with a rubber spatula until the mixture is homogeneous and resembles wet sand, then let cook for another minute, continuing to smear it with the spatula along the bottom of the saucepan. Transfer mixture to a stand mixer fitted with a paddle attachment and let sit for one minute.
With the stand mixer on medium speed, add the eggs one at a time. When all of the eggs have been fully incorporated, the dough should be thick, smooth, and shiny.
Fit a pastry bag with a large star tip. Add the choux dough to the pastry bag and pipe lines about 1 inch thick and 3 inches long onto the lined baking sheets. If you pipe them on a diagonal, you’ll be able to fit more on one sheet (see picture), but make sure to give them room to expand.
Put the baking sheets in the oven and immediately lower temperature to 375. Bake for 12 minutes, then switch the sheets, top to bottom and back to front. Bake another 12-15 minutes, until the eclairs are golden brown and puffed. Let cool on the sheets for five minutes. The shells should be used immediately or frozen and reheated in the oven.
To assemble eclairs, cut the shells in half with a large serrated bread knife. Fill the bottom half with the spicy chocolate pastry cream. Brush the top half with the melted butter and dip in the cinnamon sugar. Place the top half onto the filled bottom half. Consume immediately.