Step 1Cover the bread crumbs with water and set aside to soak.
Step 2Meanwhile, in a large skillet over medium-high heat, cook half the bacon until crispy. Remove the bacon with a slotted spoon and set aside. Pour off the bacon fat and reserve each in a separate bowl.
Step 3Cut up the rabbit: First, separate the legs and loins from the body. Cut all the meat from the bone and cut away any silverskin and fat. Coarsely chop the meat: You should have about three-fourths pound. Place the meat into a food processor and pulse several times until it is coarsely ground, being careful not to over-process. Transfer to a large mixing bowl.
Step 4Squeeze the water from the bread crumbs and add them to the rabbit meat, along with the egg, one-half teaspoon salt, one-half teaspoon white pepper, 1 tablespoon parsley and 1 tablespoon sage.
Step 5Pulse the remaining bacon briefly in the food processor, then add it to the bowl. Mix the ingredients thoroughly with your hands and then form the mixture into balls, using about 1 tablespoon for each meatball. Dredge the meatballs lightly with flour and set on a tray or baking sheet. This makes about 30 meatballs.
Step 6In a large skillet, heat 2 tablespoons of the bacon fat over medium-high heat until the fat is hot and a few drops of water spit when sprinkled in. Brown the meatballs in two batches, turning with kitchen tongs so they brown evenly, about 2 to 3 minutes. (They will be brown but not cooked through.) Set aside on a tray or baking sheet covered with a paper towel.
Step 7Wipe out the pan and add 2 tablespoons bacon fat over medium-high heat. Add the onions and leeks, turn down the heat to low and saute until soft, about 4 minutes. Add the garlic and shallots and cook an additional 2 minutes. Deglaze with wine, then add the can of tomatoes plus the juice, rosemary, the remaining 2 tablespoons of sage, one-half teaspoon salt, one-fourth teaspoon white pepper, and the thyme sprigs. Bring to a simmer, then cover and reduce the heat to low. Cook for 30 minutes, checking and stirring the sauce occasionally.
Step 8After 30 minutes, remove the pan from the heat and puree the sauce in a blender. Return the sauce to the pan, add the meatballs and the carrots and cover to coat. Cover the pan and simmer another 30 minutes, stirring occasionally.
Step 9Meanwhile, in a large pot, bring 6 quarts of water and 2 tablespoons salt to a boil. After the meatballs have simmered 30 minutes, take the pan off the heat and cook the pasta. Cook the pasta to al dente, according to the package instructions, and drain. Serve the meatballs and sauce over the spaghetti, garnishing the plates with the cooked bacon and the remaining chopped parsley.