Preheat oven to 350 °F (177 °C). Spray and line the bottom of two 6-inch cake pans with parchment paper. Set aside.
In a large bowl, whisk together flour, sugar, cocoa powder, malted milk powder, baking soda, and baking powder.
In a medium bowl, whisk together egg, buttermilk, water, vegetable oil.
Make a well in the center of the dry ingredients then pour the wet ingredients into the well and gently fold and stir the dry and wet ingredients together until a batter forms. Make sure to scrape the bottom of the bowl to make sure there's no remaining flour.
Once the batter is just mixed, divide evenly amongst the prepared cake pans.
Bake for 25-30 minutes, or until a toothpick inserted into the center of the cakes come out clean.
Let cool for 10 minutes then invert and transfer onto a wire cooling rack to cool completely.
While the cakes are cooling, make the frosting.
Beat together all the ingredients for the frosting. The consistency should be thick but spreadable.
Once the cakes are done cooling, place one layer onto a cake stand or whatever you will be serving it on. Put some frosting in the center of the cake then place the other layer on top. Gently press down.