PREHEAT OVEN: Preheat the oven to 350°F.
PREP APPLES: Peel and finely dice the apples. Place them in a small bowl with a splash of orange juice. Add the brown sugar and 1 tsp cinnamon, and then stir to combine. Set aside.
PREP DRY INGREDIENTS: In a medium-sized bowl, combine the flour, baking powder, and salt. Set aside.
BEGIN MIXING BATTER: In a large bowl (or mixer), add the 2 sticks of butter, 1 ½ cups of sugar, eggs, vanilla, and orange juice. Mix thoroughly. Gradually begin adding the dry ingredients to the wet ingredients a little at a time. Mix until just combined as to not over-mix it.
ADD APPLES: Add the apple mixture to the batter and stir until just combined. Place the batter into a large Ziploc bag, cut one corner, and pipe the mixture into the donut pan.
BAKE: Bake the donuts for 30-35 minutes.
MAKE TOPPING: In a shallow bowl, mix together the remaining ½ cup sugar and 2 tbsp cinnamon. Set aside.
Once the donuts are done baking, take them out of the oven, and allow them to cool completely. In the meantime, make the frosting.
MAKE FROSTING: Place the butter and cream cheese in to the bowl of your stand mixer and beat until light and fluffy. Scrape down the sides of the bowl. Add in the maple syrup, vanilla extract, salt, and cinnamon and mix thoroughly. Finally add the powdered sugar a little at a time and beat until well combined.
Once the donuts are cooled, remove them from the pan and toss them in the cinnamon sugar mixture. Continue with all the donuts, them drizzle some of the frosting on top.
Serve immediately. Store the remaining donuts in an airtight container at room temperature for up to 2-3 days.