Peel apples and slice in half vertically. Carefully remove the cores from the apples so as to not break them in half
Place each apple half flat side down on a cutting board and use a paring knife to hasselback the apples. You make thin slice along the arch of the apple but do NOT slice all the way through. These shallow slices will create crevices for the sugar mixture to seep into.
Line air fryer with parchment paper and transfer apple halves to air fryer flat side down
Brush apples with softened butter and sprinkle with 1 Tbsp sugar
Air fry at 375 for 10 minutes, apples will soften and start to carmelize
While apples are cooking, in a small bowl melt remaining 3 Tbsp butter.
To the butter, add sugar, cinnamon and oats and stir together
Once 10 minutes are up, open air fryer and smother apples with sugar/oat mixture. Pat down around the arch of the apple.
Air fry an additional 5 minutes.
Remove apples and top with whipped cream or vanilla ice cream. You can also remove the parchment and pour any sauce run off onto the apples.