Preheat your oven to 350˚F and line a 9x13 inch pan with parchment paper.
In a bowl, mix gluten-free flour, oat flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large bowl, use an electric mixer to cream butter and sugar until fluffy (about 1 minute). Add vanilla, applesauce, and maple syrup, and keep mixing.
Stir freshly brewed espresso into oat milk.
Alternate adding the dry mixture and the oat milk/espresso to the wet ingredients, mixing until fully incorporated. Add melted chocolate and continue mixing.
Pour the batter into the pan and smooth it out. Bake for 28-30 minutes or until a toothpick comes out clean. Let it cool completely before frosting.
For the vegan chocolate buttercream, melt chocolate in the microwave in 30-second intervals, stirring well between each interval. Let it cool until it's touchably cool.
Beat butter and powdered sugar until light and fluffy (about 3 minutes). Add cooled chocolate, vanilla, and salt, and continue mixing for another 2 minutes.
Frost the cooled cake and top it with chocolate shavings or sprinkles. Slice and savor the deliciousness!