Before you start, preheat oven to 230°C (or 210°C fan bake). Bring a medium pot of salted water to the boil.
Prep potatoes and cook in pot of boiling water for 12 minutes, until just beginning to soften. Drain well and allow potatoes to dry out well.
Transfer dried potatoes to a lined oven tray, smash edges slightly with a fork, then generously drizzle with oil and season with salt and pepper. Cook potatoes (on upper oven rack) for 25-28 minutes, until golden and crispy.
Prep beans, onion and artichoke and toss on a second lined oven tray with olives and a drizzle of olive oil and season with salt and pepper. When potatoes have 18 minutes to go, roast niçoise (on rack below potatoes) for 16-18 minutes, until tender.
Prep capers, lemon and lettuce. Set aside separately. Pat fish dry and season with salt.
Heat a drizzle of oil a non-stick fry-pan on medium-high heat. Cook fish for about 2-3 minutes each side (depending on thickness), until golden and just cooked. Place fish on a plate and keep warm. Keep same pan on heat, add butter and cook for 2-3 minutes, until bubbling, browning and smells nutty and caramelised. Add capers and cook a further 1 minute. Remove from heat and add lemon juice. Spoon caper butter over cod.
Serve potatoes with cos, roasted niçoise and caper butter blue cod.