In a large bowl, combine the butter, apple sauce, sugar and vanilla, and whisk until light and creamy. Add the egg and whisk again until combined.
In another bowl, mix together the flour, baking soda and salt. Stir into the batter and mix until combined well. Evenly spoon batter onto the prepared baking sheet, shaping into a rectangle 1-inch from the edges of the pan, and sprinkle with chocolate chips; pressing them lightly into the cookie dough.
Bake for 10 - 15 minutes, or until a nice golden colour on the top and the edges are a nice brown colour. (They will be soft when taken out, but will firm up as they cool). Cool for about 10-20 minutes. Once cooled, slice cookies into 1/2-inch strips; gently remove them with a spatula, and place them onto a wire rack to cool completely.
Notes
Nutrition calculated per cookie stick.Store in an airtight container at room temperature for up to 4 days.