1large Granny Smith apple— , peeled, cored and chopped into small pieces
In the bowl of a stand mixer, fitted with the paddle attachment, cream together butter, white and brown sugar for 3 minutes, scraping the bottom and walls of the bowl. Add egg and vanilla, mix to combine.
In a separate bowl combine flour, salt, cinnamon and baking powder.
Add flour mixture to the dry ingredients, mix until just combined. Add oats and apple and mix to combine.
Refrigerate the dough for 30-60 minutes.
Preheat oven to 350F. Line 2 baking sheets with parchment paper or Silpat. Using a 2 tbsp cookie scoop, scoop out dough and place it on the baking sheets, leaving an inch in between.
Bake for 13-15 minutes, until set.
Let cookies cool on the baking sheets for 10 minutes, then transfer to a cooling rack to cool completely.
Keep in an air-tight container at room temperature for up to 3 days.