For the sauce: 4 tablespoons butter, 3/4 cup dark brown sugar, 1 cup heavy cream, 1 tablespoon orange liquor and 1/2 teaspoon kosher salt
Toppings: 1 handful walnuts and toasted chocolate shavings
Sift together flour, cocoa powder, and salt. Create a well in the center of the dry ingredients with steep sides. Crack the eggs in the well and mix them with a fork. Gradually incorporate the flour from the sides into the eggs. Once the dough begins to form, use your hands to knead everything together. Knead for about 10 minutes, until the dough becomes smooth. Shape into a disc and cover with plastic wrap. Let it rest in the fridge for at least 30 minutes.
Once rested, divide the dough into 4 equal portions. While working on one portion, be sure to keep the others cover to prevent drying. Lightly flour each portion and roll into a rectangular shape. If you're using a pasta machine, insert the dough at the widest setting. Fold into half and run through the widest setting once more. Then feed the dough through each number setting, stopping at 5 or 6, according to your desired thickness. Then use the pasta cutter attachment to form fettucini or linguini shapes. If doing this manually, roll dough out to form a thin sheet of pasta. Lightly flour the surface, fold in half, and slice though to dough to create pasta strands. Be sure to lightly flour the strands to prevent sticking.
To make the sauce: in a saucepan, heat butter and dark brown sugar together. Once bubbling, slowly add the heavy cream while stirring. Then add the orange liqueur and salt. Stir until well combined. Set aside.
In a pot of boiling water, cook the pasta to al dente. It should take about 3-4 minutes. Drain and toss gently with the sauce. Serve with toasted walnuts and shaved chocolate on top.