In a large heavy pan, heat the olive oil over medium heat and start cooking the guanciale (or bacon) to render out the fat. After the guanciale starts to brown a little, add the onions, leeks, and carrots, and cook for 4-5 minutes. Stir in the rosemary, sage, thyme, bay leaves, red pepper flakes, and fennel. Cook for 3-4 minutes more until the onions are soft. Pour in the tomato sauce and cook the sauce until it starts to thicken, then add the red wine. Cook the sauce until the red wine is almost all evaporated, then pour in the stock. Continue cooking until the stock has reduced by a third. Add the ground rabbit and stir until all the little bits are broken apart. Simmer the sauce for about 10 minutes. This will yield about six cups of ragu.