Preheat the oven to 180ºC (fan 160ºC).
Pour the milk and cream into a saucepan, add the bay leaf and gently heat until bubbles form at the edge of the pan. Remove from the heat and set aside to infuse.
Wash the whole leek as described in the introduction, then cut into 1cm slices.
Remove the stalks from the fennel, setting aside any small tender greens for the crumb. Quarter the bulb, then roughly slice.
In a shallow ovenproof pan (or cast iron frying pan) heat 1 tbsp of the olive oil and the butter over a moderate heat. Add the prepared produce, season with salt and pepper and saute for 6-8 minutes until softened.
Sprinkle over the flour, stirring over the heat, then pour in the hot milk and cream (compost the bay leaf). Mix over the heat for 1-2 minutes until the sauce thickens. Check the seasoning adding extra salt or pepper as needed. Remove from the heat and add the grated cheese, stirring until melted.
In a bowl combine the breadcrumbs, garlic, chopped fennel greens, thyme and remaining 2 tbsp olive oil. Spoon this over the creamy mixture to create an even crumb. Place the pan into the oven and cook for 20 minutes until the crumb is nicely golden and sauce bubbling around the edges. Serve alongside pan-fried fish and roasted vegetables.
