Balsamic and port beef shanks

Ingredients

• 1 tablespoon olive oil
• 1.8 kilograms piece beef shank, cut into 6 pieces
• 1 red onion (300g), sliced thickly
• 1 stalk celery (150g), trimmed, sliced thickly
• 1/2 cup (125ml) beef stock
• 1/2 cup (125ml) port
• 1/4 cup (60ml) balsamic vinegar
• 400 grams canned diced tomatoes
• 2 sprigs fresh thyme
• 1 tablespoon light brown sugar
• 1/3 cup coarsely chopped fresh basil
• 2 teaspoons finely grated lemon rind
• 1/2 cup (60g) seeded black olives