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.
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 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 once bubbling, slowly add the heavy cream while stirring. Stir until well combined. Set aside.