Preheat oven to 190C. Heat butter in a saucepan over medium-high heat until foaming, then add flour and stir continuously until sandy coloured (1-2 minutes). Gradually add combined milk and cream, whisking continously until smooth and incorporated (4-6 minutes). Bring to the boil, stir in Taleggio and season to taste.
Steam Brussels sprouts in a steamer until almost tender (5-7 minutes), then drain and transfer to a buttered 2-litre ovenproof dish.
Pour sauce over sprouts, scatter with thyme and bake until golden and bubbly (20-30 minutes). Serve hot.
This recipe is from the May 2013 issue of Australian Gourmet Traveller.