To start, chill a big lined sheet pan inside the freezer for at least 1 hour.
Once the sheet is cold, begin rolling some ice cream balls. Heat the ice cream scoop slightly in hot water. Then, roll the balls and place them in the lined tray immediately. Don't remove the cold tray from the freezer.
Prepare the bread or cake slices
Next, remove the crust from the slices of bread. Set the crust aside for another use. You don't have to remove the crust from the cake because it's not as hard.
Then, use about two slices of crustless bread or cake. Place them on a piece of plastic or saran wrap. Allow their edges to slightly overlap.
Use a rolling pin to flatten them on the plastic sheet. It will also help seal the edges together.
Shape the ice cream balls
Place the ball of ice cream in the middle of the flattened slices of cake or bread.
Then, use the plastic sheet to fold the slices over the ice cream ball. Twist the edges of the plastic sheet so that the ball gets tighter and tighter. That will help seal the bread or cake layer into place.
Finally, tie a knot in the plastic to secure the tight ball. Place the ice cream balls back into the fridge and allow them to harden.
Make the batter
To make the tempura batter, place the flour and egg in a large mixing bowl. Whisk until you have a semi-thick batter.
Then, slowly add water while whisking until you have the right consistency. The batter should be completely lump-free, thick, but runny.
Deep fry the ice cream balls
Heat the vegetable oil in a large pot until it reaches 360ºF (180ºC).
Once your ice cream balls have hardened, dip each in tempura batter.
Immediately fry one ice cream ball at a time. Turn the ball frequently so that it browns on all sides.
Remove the fried ice cream balls and drain them on pieces of kitchen towel.
Dust the ice cream balls with powdered sugar and serve them immediately.