Mussels in Cider with Saffron Velouté Sauce

Ingredients

• 2½ tbsp extra-virgin olive oil
• 2 kg black mussels, scrubbed
• 200 ml dry apple cider
• 120 gm butter, coarsely chopped
• 2 leeks, washed thoroughly, halved lengthways and thinly sliced
• 80 gm plain flour
• 1 tsp saffron, soaked overnight in 2 tbsp hot water
• ½ cup (loosely packed) flat-leaf parsley leaves, to serve