Melt the butter in a pan until foaming then add the bacon pieces. Fry until crisp. Add the garlic, cook briefly then add the flour and mustard powder. Cook away the raw flavour then add the milk gradually until all incorporated. Top up with the beer and cook for 5 minutes on medium. Season with salt and pepper. Turn the heat right down and add the cheeses in batches (to avoid splitting). Once the final batch has been added remove from the heat and add to the macaroni. Stir to combine then pop in the fridge for a couple of hours to firm up.
Remove the macaroni cheese from the fridge and grab a lump in your hand. It should be somewhere between a ping pong and a tennis ball. Roll this lump in the flour, then dip into the egg, and finally roll in the diorite pieces.
Deep fry until crisp (but not browned) and heated through. This should take about 30 seconds. Drain on kitchen towel and serve.