Transfer the feta and the pancetta into a bowl and mix well with a fork.
Combine the flour and a few tablespoons of the water in a medium bowl until a thick paste is formed. Add the rest of the water gradually, until you get a smooth slurry.
Place toast crumbs into a large plate.
Form a flat disk and put about half a tablespoon of filling in the center. Wrap the filling with the risotto and form a ball.
Let the ball rest on a clean surface and continue until all the risotto is gone.
When done, place arancini in the fridge for 15 minutes to firm up.
Fry arancini in batches, about 4-5 each batch so that the temperature of the oil doesn’t drop down very much. Cook for 2 minutes each side, flipping them gently with a slotted spatula.
Remove with the spatula when golden brown and transfer to a paper towel to absorb the extra oil.
You may want to add half a cup grated parmesan to your risotto when still warm, since this will help the balls hold their shape better.