In a small bowl, whisk together the pumpkin puree and the egg yolk.
If using a stand mixer fitting with the paddle attachment, combine flours and egg yolk/pumpkin in the mixer. Begin mixing on a slow speed, adding small amounts of water as you go, if needed, until the mixture comes together into a ball. Knead on medium for 5 minutes
If kneading by hand, mix flours and dump out onto the countertop. Make a well in the center of the flour pile and add the egg/pumpkin mixture to this well. Begin incorporating flour into the egg/pumpkin mixture, adding a bit of water as needed as you go. Knead the dough by hand on the countertop for 5-10 minutes.
Check that the dough is sufficiently kneaded by cutting the dough in half. You should see many small air pockets inside the dough. If you don't see these, continue kneading.
Wrap the dough in plastic wrap or cover and set aside to rest for at least 30 minutes. The dough can also be made in advance and at this point can be wrapped and left in the fridge for 1-2 days.
Roll out your pasta, either using a shape extruder, a pasta roller for long noodles or ravioli, or by hand using the cavatelli method.
Cook pasta in salted rapidly boiling water until the pasta begins to float, 3-4 minutes. Reserve 1/2 cup of the pasta water for the sauce.