Preheat oven to 350 degrees and lightly grease a 9 x 13″ pan.
In a stand mixer (or by hand), beat the eggs then add in the room temperature butter. Mix until combined.
Mix in the applesauce, sour cream, and milk as well as the vanilla. Mix on medium-low speed for 1-2 minutes or until smooth.
In a separate bowl, stir together the dry ingredients: flour, sugar, baking powder, and salt.
Add the dry ingredients to the wet ingredients in thirds, combining between each addition. Mix just until incorporated.
By hand, gently stir in 1/3 cup of chocolate chips.
*Make streusel. See below.*
Spread HALF of the cake batter into the bottom of your 9 x 13 pan until an even layer is formed.
Dollop HALF of your streusel mixture on top of the initial layer of cake batter, spreading it out the best you can without stirring it in.
Top the layer of streusel with the remaining cake batter, spreading into an even layer and covering the streusel.
Dollop the remaining streusel over the second layer of cake batter, again spreading into an even layer the best you can. Sprinkle a tablespoon or two of chocolate chips on top.
Bake for 30-35 minutes or until toothpick comes out clean.
Once cooked, turn off oven, remove cake from oven and top with marshmallows, graham crackers crumbs, and Hershey bars. Return to the turned off oven for 2-3 minutes to melt the toppings.
Streusel
Stir together the brown sugar, graham cracker crumbs, and melted butter.