Place a large saucepan of water on the stove and bring to the boil.
In a large fry pan, cook the pancetta until it is crispy. Remove from the pan and set aside. Leave any residue from the pancetta in the pan. Then add the fennel, onions and fennel seeds and cook on medium heat for a few minutes until softened. Add some of the garlic oil if needed.
Once the fennel and onions have softened, add the pancetta back to the pan and mix through. Remove from the heat and set aside.
Cook the pasta according to packet instructions, then drain and place back into the saucepan. Mix in the fennel and pancetta.
Preheat oven to 180 degrees Celsius, and lightly spray and baking dish (min.1.5L capacity) with come cooking spray.
To make the white sauce, place the milk in a medium saucepan, cut the onion in half leaving the skin on, and add to the milk. Add the bay leaves, cloves and nutmeg and heat on medium until the milk is just below boiling point. Remove from the heat and allow the flavours to further infuse for a few minutes. Then remove the onion, bay leaves and cloves. Ensure the milk doesn’t cool down too much, it will need to be warm for the next step.
In another medium saucepan (or tip the infusing milk into a bowl or jug and use the same pan again), melt the butter on medium heat. Add the flour and whisk until combined. Remove from the heat and add the warm infused milk in a steady stream, whisking continuously until there are no lumps.
Place the saucepan back on medium-high heat, and stir continuously with a wooden spoon or spatula for about 10 minutes, or until the mixture has thickened and bubbles are appearing on the surface.
Once the white sauce has thickened, turn the heat down, and add the cheddar and 100g of the parmesan. Mix until the cheese has melted into the sauce.
Remove from the heat and tip the white sauce into the pasta and mix until everything is well combined.
Transfer the pasta to the prepared baking dish, and sprinkle the top with the panko bread crumbs and the remaining parmesan.
Bake for about 30 minutes, or until the top is crisp and golden.
Sprinkle with chopped fennel fronds before serving if desired.