Step #1 Using a meat tenderizer or a heavy skillet, lb the chicken breasts between two sheets of plastic wrap until flat, about a 1/4-inch thickness.
Step #2 Place the milk, flour, eggs, & bread crumbs in separate shallow baking dishes.
Step #3 Spice up the eggs with a pinch of salt.
Step #4 Dip each breast in the following order; milk, eggs, flour (shake off excess), & bread crumbs (press down firmly while coating with bread crumbs).
Step #5 In a large skillet, melt the butter with the olive oil over medium-high heat until sizzling.
Step #6 Arrange the chicken breasts in the pan without crowding, cooking in batches if necessary.
Step #7 Reduce the heat, & cook the chicken until golden brown & the juices run clear when poked with a sharp fork, 3 to 5 mins per side.
Step #8 Remove to a baking sheet lined with paper towels; pat off excess oil.
Step #9 Place 1/2 c of the warm tomato sauce in the bottom of a 9- by 13- by 2-inch baking dish.
Step #10 Add 3 of the cooked breasts to the baking dish; cover with 1/2 c of the warm tomato sauce & half the sliced mozzarella.
Step #11 Repeat with the remaining chicken breasts & sauce, and top this with mozzarella.
Step #12 Transfer to broiler & broil until the cheese is melted & golden brown, about 5 mins.