Heat oil in deep fryer or heavy skillet to 375°F.
Slice leftover pork tenderloin into ½" cubes and wrap each one in mozzarella cheese.
Separate your leftover risotto into 2" balls and one by one press them into your palm, place a mozzarella-wrapped pork tenderloin cube into the middle, shape the rice around the pork tenderloin and roll into a ball.
Combine milk and eggs in a bowl and whisk until smooth.
Coat each rice ball in flour, dip in egg wash and cover in breadcrumbs. Repeat this process again if necessary.
Fry rice balls for 2 minutes or until the breading is golden brown.
Drain on paper towels and serve with marinara or your preferred dipping sauce.