Preheat your oven to 350 degrees
In a stand mixer, cream together butter and 1 1/4 C brown sugar with 3/4 C white sugar
Add eggs one at a time and continuing mixing
Add gluten-free flour, salt, baking soda, baking powder and cacao powder in another bowl then to the wet ingredients until just mixed
Combine oats, orange extract, vanilla extract and water in a bowl and let them sit 2 minutes then add it to the other cake mix ingredients
Gently stir in 6 ounces milk chocolate chips
Pour batter into a greased 9x13 cake pan
Sprinkle 6 more ounces milk chocolate chips to the top of the cake before baking
Bake at 350 degrees for 35 minutes or until toothpick inserted in the center comes out clean or just crumby but not wet
Meanwhile, prepare the frosting by combining 6 T melted butter, 1 1/3 C sugar, cream, milk and 1/4 tsp. orange extract in a pot and cook over low to medium heat
Bring to a boil then reduce heat to low and add mini marshmallows and 6 ounces milk chocolate chips
Stir until smooth then pour immediately over the cooled cake, do not allow the frosting to cool first