Pre-heat the oven to 180°C.
Melt 50g butter in a pan, add flour, and cook for 2-3 minutes.
Whisk in milk gradually until the sauce is smooth and thickened.
Stir in mustard, Worcestershire sauce, and grated cheddar cheese.
Soften sliced leeks in 25g melted butter for 2-3 minutes and add to the sauce.
Fry brioche cubes in the remaining 25g butter until golden.
Boil broccoli and cauliflower florets for 2-3 minutes then drain.
Combine vegetables, sauce, and brioche in a dish, topping with poaching cheese and brioche.
Bake in the oven for 25-30 minutes.
Whisk oil, vinegar, Dijon mustard, and lemon juice together for the dressing.
Toss lettuce leaves with the dressing.
Serve the bake with tenderstem and romanesco broccoli and the side salad.