Pot roast pork shoulder with mushrooms, port and chestnuts

Ingredients

• 1.2 kilogram boneless pork shoulder, rind removed
• 1/2 cup (125ml) port
• 3/4 cup (180ml) vegetable stock
• 1 tablespoon finely grated orange rind
• 1/2 cup (125ml) orange juice
• 1/4 vanilla bean, split
• 90 gram swiss brown mushrooms
• 90 gram fresh shiitake mushrooms
• 3 portobello mushrooms, sliced thickly
• 5 gram dried porcini mushrooms
• 1 clove garlic, sliced thinly
• 2 shallots, halved
• 125 gram canned chestnuts, drained