Preheat oven to 400 degrees and grease a donut pan well with baking spray.
Mix flour, sugar, baking powder, nutmeg, and salt together.
Add in the egg, buttermilk, vanilla extract, and butter. Mix until just combined.
Spoon or pipe the batter into each donut cavity, filling about 3/4 of the way full (you will have enough batter for about 8 donuts).
Bake for Bake for 10-12 minutes, or until the donuts are lightly golden and 'spring' back when touched.
Allow to cool for a few minutes, then remove the donuts from the pan and allow them to continue cooling on a wire rack (about 10 minutes).
While cooling, melt the butter in a shallow dish (one large enough the whole donut can fit in it).
Mix the sugar and cinnamon together in a separate bowl.
Dunk both sides of the donut in the melted butter. Immediately roll the donuts in the cinnamon sugar mix, making sure it is well-coated.
Allow to finish cooling on a wire rack.
With a mixer on medium speed, beat the heavy cream until it begins to thicken. Add in powdered sugar and vanilla, and continue to beat until it reaches a whipped-cream consistency.
Assemble the Strawberry Shortcake Donuts right before serving. Cut the donuts in half and spoon on whipped cream and strawberries.
Enjoy!