Whole Wheat Apple, Walnut, Chocolate Chip Cookie Cake

1 Preheat oven to 350°F.
2 Melt the butter in an 8-inch cast iron skillet over medium-low heat.
3 Once melted, stir in sugar and vanilla extract, then remove from heat and whisk until thoroughly combined. Allow the mixture to stand and cool for about 5 minutes. (If the mixture is hot when you add the eggs, they will scramble.)
4 Add the egg, and whisk into the mixture until smooth.
5 Then add the applesauce and cinnamon. Stir to combine.
6 Sprinkle in the flour, baking soda and salt. Stir carefully until all of the dry ingredients are incorporated.
7 Add the chocolate chips and walnuts, and fold the mixture together.
8 Smooth the mixture on top.
9 Place the skillet in the oven, and bake for 25-30 minutes or until dry on top, but slightly soft in the center. (My oven takes a bit more time, so please check yours at the 20 minute point to make sure everything is all right and still delightfully gooey.)
10 Remove from oven and allow to cool for 15 minutes.
11 Serve warm, and enjoy with a glass of cold milk or a scoop of ice cream.