Preheat the grill to its highest setting.
Mix crushed garlic with 20g butter and spread over Portobello mushrooms.
Season mushrooms with salt and pepper and grill for six minutes.
Heat olive oil in a saucepan and sauté leeks for 3 minutes until browned.
Add garlic and sliced mushrooms and sauté for two more minutes.
Stir in 150ml double cream and mustard, then cook gently for one minute.
Stir in parsley and keep the sauce warm.
Steam 100g broccoli florets for six minutes until al dente.
Toss steamed broccoli in 15ml olive oil and season with salt and pepper.
Arrange broccoli around a plate, pour sauce in the middle, and top with grilled mushrooms.