In a large bowl, whisk together the cocoa and melted butter. Stir in sugar until combined. Stir in eggs, one at a time, mixing well after each. Stir in vanilla. Fold in flour JUST until you no longer see flour streaks in the batter. Gently fold in hot fudge sauce (you may need to heat it just enough to spoon/pour out of jar). Fold in candy.
Prepare frosting: In the bowl of a mixer, beat butter, vanilla, and cream on medium low until combined. With the mixer on low speed, beat in powdered sugar and malt powder until just barely mixed. Increase speed to high and beat for one minute. Fold in crushed candy and spread frosting on cooled brownies.