Cider-Roast Rainbow Trout with Leek and Prosciutto

Ingredients

• 30 gm butter, coarsely chopped
• 80 ml olive oil (1/3 cup)
• 1 leek, thinly sliced
• 1 garlic clove, finely chopped
• 10 wide prosciutto slices
• 250 gm coarse sourdough breadcrumbs (3½ cups)
• ¾ cup coarsely chopped flat-leaf parsley, plus extra to serve
• Finely grated rind and juice of 2 lemons
• 8 rainbow trout (about 300gm each), butterflied (see note)
• 2 Spanish onions, thinly sliced into rings
• 300 ml dry cider
• 300 ml chicken stock