Preheat oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper or a silicone baking mat.
Combine dry ingredients and stir until well mixed. Add apple, peanut butter and milk to dry mix and knead until all ingredients are well combined.
Form dough into flat logs about 5 inches wide and 1 inch high. Bake on prepared baking sheet for 15 - 20 minutes.
Remove from oven and allow to cool for 10 minutes then cut logs into 1 x 1 inch squares.
Place squares back onto baking sheet and bake for 10 minutes, until the pieces are dry and crunchy.
Cool and refrigerate.
1 to 2 dozen.