Using a 12 ounce mug (1 1/2 cups capacity)
Build the custard: In a large bowl, add egg, milk, brown sugar and pumpkin pie spice. Whisk until as smooth as possible. Add fruit cocktail, a pinch of salt and stir.
Soak bread: Add bread to the custard and stir until combined. Allow to rest for 5 minutes.
Prepare the mugs: Spray the insides of two 12-ounce mugs (1 1/2 cups capacity) with cooking spray. Spoon sugar into both mugs; tilt and tap the sugar to coat the bottom and sides of the mug. Tap out excess sugar.
Fill the mugs: Divide soaked bread in half and gently press into both mugs. Top both with equal amounts of butter. Place mugs in the microwave for 3–3 1/2 minutes. Remove and allow mug to cool slightly, then eat.