To make the sauce: Heat the olive oil in a small pan over medium heat. Add the garlic and saute until beige. Add the shallot and cook until translucent and the garlic is a light golden color. (Don't let the garlic burn or it will taste bitter.) Add the pepper flakes and saute for about 10 seconds more. Add the tomatoes and simmer for 15 to 20 minutes.

To make the croquettes: Preheat the oven to 200 degrees F.

In a saucepan, boil the potatoes until tender. Drain the potatoes, place on a sheet pan, and allow to dry in the oven for about 5 to 10 minutes. Pass the potatoes through a food mill or ricer (passatutto) and let them cool in a bowl. Stir in the egg yolks and the Parmesan cheese. Season with the salt and pepper.

Place 2 tablespoons of the potato mixture in the palm of your hand and make a small ball. Make an indentation in the center with your thumb. Place 3 cubes of the mozzarella in the center and bring up the sides of the potato mixture to cover it. Pinch it well and then roll it between the palms of your hands until it forms a stick about 2 1/2 inches long. Repeat the process. Once you have all the potato sticks done, roll them in the egg whites, then in the bread crumbs. Remove excess crumbs and again roll them lightly between the palms of your hands to set the bread crumbs.

Pour vegetable oil to a depth of 2 inches into a skillet and heat until a drop of batter dropped into the oil rises right away. Deep fry the croquettes until golden brown, drain on paper towels, and serve immediately with the sauce on the side for dipping.