cheese and leek chicken gratin

chicken breast 71.0% , Rarebit Cheese Melt 17.0% , full fat soft cheese 6.0% , cheddar 3.0% , brown ale 1.5% , cream 0.8% , water 0.4% , dijon mustard 0.2% , corn starch 0.1% , salt 0.0% , lemon juice 0.0% , cracked black pepper 0.0% , leek 9.0% , cheese 9.0% , breadcrumbs 0.0% , rapeseed oil 0.0% , leek 0.0% , cheddar 0.0% , potato starch 0.0% , salt 0.0% , cracked black pepper 0.0% , spinach 2.0%