Peel, core and dice apples.

Heat up a sauce pot over medium heat. Add butter and sugar, mix well. Add diced apples and apple pie spice. Mix well, cover and cook until apples are softened.

Take off the lid and stir in flour. The mixture will thicken. Mix and cook for about a minute. Take off heat.

Preheat oven to 350 and grease a doughnut pan.

In a large mixing bowl, whisk eggs, sugar, buttermilk, melted butter and vanilla together until smooth.

Sift in all dry ingredients and whisk until all incorporated.

Add apple pie filling mixture and mix well using a spatula. (The mixture should not get much thinner.)

Pour the batter into a piping bag. (You may have to use a large piping bag or do it in two batches.)

Cut the tip off both piping bags, leaving only about 3/4 inch opening.

Squeeze batter into the doughnut cups of the pan, in the half-circle motion. Make sure there is an even amount of batter all around.

Bake for 11-12 minutes and let doughnuts cool on the wire rack, just until the doughnuts cooled enough to be handled.

Melt butter in one little cup and mix sugar and cinnamon in a shallow bowl.

Brush the top of the doughnut with a little butter and then dip it into the cinnamon sugar mixture, cover it evenly. Place back on the wire rack and repeat with all doughnuts.