Preheat oven to 450F and prepare two lined baking sheets with wire racks. For the meatballs, mix all ingredients in bowl and combine well with your hands. Form into 2-inch round meatballs. Place meatballs on the wire racks and bake for 40 minutes, and rotating trays while switching top and bottom trays halfway through baking. After baking, reduce oven temperature to 350F.
Some farmers sell heart by the pound. Others sell it whole. If you have a sliver of the whole heart (in your 1lb package, or similar), it may well be trimmed for you! And you can go ahead and prepare evenly sized cubes and pulse it in your blender to prepare your ground
While the meatballs are roasting, prepare sauces. For the marinara, add lard to a pan on medium heat. When shimmering, add onion and cook 6 minutes. Add garlic, pepper flakes, oregano, thyme and salt. Cook for another minute until it's fragrant, than add tomatoes and mix well. Increase heat and bring to a simmer, then reduce heat to medium-low for another 15-20 minutes to thicken a bit. For the pesto, combine all ingredients in a food processor and blend into a paste. Cover and refrigerate if not using shortly.
Confirm that the oven temperature is 350F. Slice your bread lengthwise and place over a large sheet of foil (so sandwiches can be wrapped). Cover the bottom piece of bread with a thick layer of marinara and meatballs. Cover with provolone. Spread a thick layer of pesto on the bottom side of the upper bread and place on top of provolone to cover sandwich. Wrap loosely in foil and bake until the cheese has completely melted and the bread is warm and toasted, about 20 minutes. Serve warm.
On the other hand, if you have a whole heart, it's likely close to 3 lbs and I suggest you consider using heart exclusively and omitting the other meats for the meatballs.
To prepare a whole heart, stand it up on the heart shaped bottom end and slice down the side. Once it's open, trim any connective tissue off the inside of the top of the heart (reserving the thick fat on the outer side of the top of the heart). Next, trim all the tubes and silverskin from the inside of the heart. Now it's ready for any preparation.
To blend the heart, cut into large, evenly sized cubes and pulse in a food processor until it resembles ground beef. Voila, it’s ready!