Drain the soaked chiles and place in a blender with the roughly chopped tomatoes, toasted pumpkin seeds, the epazote sprig if using, and 1 cup of the reserved turkey broth. Blend on high for 1 to 2 minutes until completely smooth. The sauce should be a deep reddish brown, thick and intensely fragrant. For a smoother, more refined result pass through a fine mesh strainer pressing all the solids through with the back of a spoon. This is optional but produces a sauce closer to the standard of preparation that would have been served at Montezuma's table.