THE PASTA DOUGH:
1 1/2 cups all-purpose flour
1/4 cup cocoa powder, plus more for dusting
3 tablespoons sugar
Pinch of salt
3 large eggs
Water as needed
THE CHOCOLATE PASTRY CREAM FILLING:
1-1/2 cups milk
1/4 teaspoon vanilla paste
1/4 cup sugar
3 egg yolks
7-1/2 teaspoons cornstarch
1 tablespoons unsalted butter
1/4 pound hazelnut butter, thoroughly stirred
1/4 cup heavy cream
1/4 cup milk
1-1/2 teaspoon sugar
2.5 ounces bittersweet chocolate, roughly chopped
1-1/2 teaspoon unsalted butter
THE POACHING LIQUID:
10 cups water
2-1/2 cups sugar
1. For the pasta dough, sift the flour, cocoa powder, sugar, and salt into a large mixing bowl and whisk to blend. Make a well in the center of the dry ingredients and place the eggs in the well. Using a fork, slowly incorporate the eggs into the flour, until all the eggs have been absorbed. Add water if needed to make a firm dough. Transfer the dough to a work surface and, using the palm of your hand, lightly knead the dough for 3 to 4 minutes. If the dough is sticky, sprinkle a little flour on the kneading surface. The dough is ready if, when you make an impression in it with the tip of your finger, the dough bounces back. Shape into a disk and tightly wrap in plastic film. Let the dough rest for at least 30 minutes in the refrigerator.
2. Meanwhile, make the pastry cream: In a medium saucepan, combine the milk and vanilla. Place over high heat and bring to a low-boil (be careful not to scorch the milk). Meanwhile, using a whisk, in a medium bowl, whip the sugar and egg yolks until pale yellow and frothy, about 2 minutes. Slowly add the cornstarch while whisking and whisk to dissolve any lumps.
3. Temper the egg yolk mixture by pouring a little of the steaming milk into the yolks, whisking to incorporate. Whisk the egg yolks into the remaining milk in the pan, set the pan over medium heat, and whisk quickly and constantly until the mixture thickens and comes to a boil, then whisk for another minute. Remove from heat, add the butter and stir until incorporated. Transfer the pastry cream to a bowl and place plastic wrap directly against the cream to prevent a skin from forming on top. Refrigerate until fully chilled, about 2 hours.
4. Once the pastry cream has chilled, Add the hazelnut butter to the pastry cream and stir to incorporate. Return to the refrigerator and chill for at least 30 minutes.
5. Divide the pasta dough into 4 pieces. Using a pasta machine, one at a time, roll out each piece from the widest to the thinnest setting. Keep the remaining dough covered to prevent it from drying out.
6. To make the ravioli, dust a work surface with flour. Place one pasta sheet on the work surface. Starting about 2 inches from one end, place a teaspoon of filling every 4 inches down the pasta strip, ending about 2 inches from the other end of the strip. Brush the pasta dough with water, fold the dough over, and press to seal, being careful not to trap air inside the ravioli (or they will burst during cooking). Cut the ravioli. Press the edges together and squeeze to make the edges of the dough as thin as possible. Set the finished ravioli on a baking sheet lined with parchment and sprinkled with flour, to prevent sticking. Repeat with the remaining dough. You should get at least 30 or more ravioli. Refrigerate until ready to cook.
7. For the sauce, bring the heavy cream, milk, and sugar to a simmer in a small saucepan. Remove from the heat, add the chocolate, and stir until melted. Then add the butter and stir to incorporate.
8. To cook the ravioli, bring the water and sugar to a boil in a large pot and boil until the sugar has dissolved. Add the ravioli to the pot and cook until al dente, about 8 minutes.
9. Meanwhile, gently reheat the chocolate sauce.
10. To serve, remove the ravioli with a slotted spoon, letting the excess liquid drain, and arrange 4 ravioli on each plate. Drizzle the sauce over each plate. Serve immediately.