I have used mulberry puree for the doughnuts, although any berry puree can be substituted. To make the puree, I weighed the berries, then blitzed them to a puree with a hand held blender. Defrosted smoothie cubes could be used to speed up this process. I use two standard size doughnut pans to bake the doughnuts. If using different sized pans then adjust the baking time accordingly.