Roast fillet of beef with stir-fried greens

Preheat oven to 200 ºC. Heat butter in a heavy-based frying pan. Add fillet and brown for 2-3 minutes.
Mix 80 ml mustard, 30 ml soy sauce, half the garlic and 30 ml oil together to form a paste. Spread on to the fillet to coat well. Place in a greased roasting pan and roast in the oven for 20 minutes. Remove from oven and set aside to rest for 5 minutes.
Heat rest of oil in a large frying pan or wok. Add remaining garlic and 5 ml mustard and stir-fry for 30 seconds. Add mangetout and celery and stir-fry for 1 minute. Add bok choi and spring onions, cut into 2 cm pieces, and continue to stir-fry until bok choi has wilted. Stir in lemon juice and remaining 5 ml soy sauce and season to taste with salt and freshly ground black pepper.
Slice fillet and serve with vegetables, buttered baby potatoes and extra mustard. Serves 4-6