In a small bowl, combine the yeast and milk and stir well. Let activate, about 5 minutes until bubbly.
In the bowl of a stand mixer fitted with the dough hook attachment, mix the flours, cold water, salt, oil, and yeast mixture at low speed until combined, about 10 minutes.
Increase the speed to medium-low and continue to mix until the dough is smooth and elastic and pulls away from the sides of the bowl, about 5 minutes.
Add the pumpkin seeds and mix at low speed until incorporated, about 1 minute.
Cover the bowl tightly and refrigerate until the dough has doubled in size, about 12 hours (overnight is easiest).
On a lightly floured work surface, using your hands, roll out the dough into a log, about 2 inches (5 centimeters) wide, being careful not to overwork it to preserve the air bubbles that help create a more open-crumb structure.
Using a bench scraper or a sharp knife, divide the dough into 8 equal pieces.
Working with one pieces at a time, press down on the dough with the palm of your hand, then stretch it until it is about three times as long as it is wide. Imagine each piece as 3 connected squares. Take one end square of the dough and fold it over the middle square, then fold the other end square over the middle square as well. You should now have a small, 3-layer dough package.
Lightly press down with your palm to flatten it to half its original height. Finally, use your fingertips to gently press along the seam to seal it. Repeat with the remaining pieces.