1.In a large saucepan, combine fennel, leek, cream and milk. Simmer with lid on for about 15 minutes or until fennel is tender. Transfer fennel and leek to six shallow 1-cup (250ml) ovenproof dishes. Reserve cream mixture.
2.Preheat oven to 220°C (200°C fan forced).
3.Melt butter in same pan. Add flour and stir about 2 minutes or until mixture bubbles and thickens. Gradually stir in hot cream mixture. Continue stirring until sauce boils and thickens. Season to taste.
4.Pour sauce over fennel, and sprinkle with combined cheeses, breadcrumbs and reserved fennel fronds. Bake for about 15 minutes or until browned lightly.