Preheat the oven to 170°C.
Melt the butter in a casserole dish over low heat.
Place fennel cut-side down with trimmings, season, and increase heat.
Add vermouth and pastis, cover with foil and lid, and bake for 30 minutes.
Turn fennel over and bake for another 30 minutes until tender.
Preheat the grill to high.
Place fennel in a warm oven-proof dish, cover, and keep warm.
Strain cooking juices into a pan, warm through, and add 45g of parmesan.
Blend the sauce until smooth and creamy using a hand blender.
Pour sauce over fennel, sprinkle with remaining cheese, and grill until golden.
Serve with extra parmesan for sprinkling.