Heat the oven to 200°C (180°C fan) 400°F (350°F convection).
Put the butter into a small frying pan over medium heat while you peel and slice the garlic.
Add the garlic slices to the pan along with the fennel seeds, and cook gently while you prepare the fennel.
Cut the very ends off the fennel stalks, keeping any feathery fronds to use as a herb at the end of cooking.
Chop the fennel bulb in half from root to stalk, then cut the root ends off. Then cut each half into slices around 5mm (¼ inch) thick from root to tip.
Lay the fennel in a deep-sided ceramic or glass baking dish, around A4 size.
When the garlic is gently golden and soft, add the wine to the pan and allow it to bubble for a minute before adding the stock cube and 100ml (half a cup) boiling water.
Use a spatula to squish the cube into the liquid until combined, then take off the heat and pour it over the fennel slices. Tightly cover the fennel dish with foil, then bake for 45 minutes until the fennel is tender.
When the fennel is ready, either season with lemon zest and juice and a final splash of wine and serve immediately or use as a base for the cod. Once the fennel is cooked, it can sit in the fridge for 4 days and can be reheated in the oven.