Preheat oven to 350°F.
Place the cookies in a food processor and blend until you have an even sandy texture.
Place the cookie crumbs, melted butter, sugar and salt in a medium bowl and mix until combined. Remove ¼ cup of crumbs and set aside for the topping.
Place 4 x 4 inch mini tart pans or 1 - 8 inch tart pan with a removable base on a cookie sheet lined with parchment.
Divide the crumb mixture evenly between the pans and press into the base and up the sides.
Bake in the oven for 15 minutes.
In the meantime, place the nuts in the food processor and pulse until chopped.
Add the nuts to the ¼ cup of crumb mixture, stir and set aside.
Peel apple and cut into small cubes. Place in a medium bowl.
Add the dulce de leche and cookie butter to the chopped apples and stir to combine.
Once the cookie crumb bases come out of the oven, divide the apple mixture between the four mini tart pans, spreading to the edges.
Sprinkle the crumb nut mixture on top of each tart and bake for 25 minutes.
Remove from oven and allow to cool slightly before serving.
