Preheat oven to 350°F. Spray a 9-inch cake pan or square pan with non-stick spray.
Melt the butter in a medium saucepan over medium heat. You want it to it turn a little bit darker {a golden color} but not burn. This takes about 5 minutes.
Remove from heat and stir in applesauce.
Then add sugar, and stir until completely combined. Let sit for 10 minutes to cool.
Once cool, whisk in egg and vanilla, and stir until completely combined.
Stir in salt & flour, and mix until just combined. Try not to over-mix.
Fold in chocolate chips.
Pour into prepared cake pan, and bake in preheated oven about 20 minutes or until the edges are lightly browned and pulling away from the sides of the pan.
Let cool in the pan 10 minutes then take out & transfer to a cooling rack to cool completely.
Once completely cool, ice cake with icing.
Enjoy!
Notes
*A flax egg is 1 tablespoon flax meal + 3 tablespoon water