Preheat oven to 350F and line a 9" square pan with parchment paper.
Place your butter in a large, microwave-safe bowl and microwave until melted.
Stir in cocoa powder.
Add malted milk powder and sugar, stir well.
Stir in your milk and your vanilla extract.
Add eggs and egg yolk, stirring until well-combined.
In a small, separate bowl, whisk together the flour, baking powder, and salt. Gradually stir into the butter mixture until completely combined.
Spread evenly into prepared pan and bake on 350F for 35 minutes, or until toothpick inserted in center comes out mostly clean or with few dry crumbs.
Allow brownies to cool before adding fudge topping.
Fudge Topping
First, crush approximately 1 ½ cups of your malted milkballs and set aside. Don't obliterate them to smithereens. I place mine in a Ziploc bag and then smack them a few times with a rolling pin, so that I have some small pieces and some large chunks.
Combine chocolate chips and heavy cream in medium saucepan and set to medium heat.
Stir frequently until chocolate is completely melted and well-combined with the cream.
Remove from heat and allow to cool for 5 minutes.
Once 5 minutes has passed*, pour the ganache over the brownies. Allow it to cool on the brownies for 2-3 minutes and then generously sprinkle your uncrushed malted milk balls and then your crushed milk balls
Wait for ganache to cool and harden to a fudge-like consistency before cutting and serving. The fudge will harden at room temperature, but it will be much faster if you place it in the fridge for about 30 minutes. However, after solidifying the ganache in the refrigerator, I like to bring these brownies back to room temperature before enjoying.
Notes
*If the ganache seems too runny at this point and is too thin, wait another 5 minutes before pouring