Osso buco with spinach polenta

Ingredients

• 6 pieces (1.3kg) veal osso buco
• 2 tablespoons plain flour
• 20 grams butter
• 1 tablespoon vegetable or olive oil
• 1 small celery stick, finely chopped
• 1 small carrot, finely chopped
• 4 cloves garlic, crushed
• 1 1/2 cup passata (italian cooking sauce)
• 1 3/4 cup chicken stock
• 2 tablespoons chopped flat-leaf parsley
• 2 teaspoons finely shredded lemon zest
• Spinach polenta
• 3 cups chicken stock
• 1 1/2 cup polenta (corn meal)
• 100 grams baby spinach leaves, coarsely shredded
• 1/2 cup freshly grated parmesan