While the donuts are baking for 14 to 18 minutes at 350F / 176 C, it is time to make the optional cream filling. If you have a pastry injector, I highly recommend using it to speed up the filling process an make it a whole lot less messy.
Combine all of the cream filling ingredients together in a bowl. I hand-mix mine, but using a stand mixer would also speed up the process. Think of hand mixing as both a great arm workout and practice for living in an off the grid situation - if you're like me, you do not want to mess with lugging out the stand mixing and then cleaning it afterwards.
If your cream filling mixture looks a bit thick and lumpy like in the photo, add just a little more milk to garner a creamy consistency that will flow through a pasty injector, pastry bag, or a sandwich baggy that is doubling as a pastry bag.