Heat oven to 200C/180C fan/gas 6. Use a large knife to hasselback the potatoes; cut incisions in each potato making sure you don’t cut through to the base, and keep the cuts as close together as possible. Toss the potatoes in oil and some seasoning in your largest roasting tin (an oven tray is ideal – line with parchment first if it’s old). Roast for 20 mins.
Butterfly the prawns by cutting a line down the back of each one, through the shell from the base of the head to the top of the tail. Pull out the black line of intestine from each one. Clean the mussels under cold water, pulling off any hairy or stringy bits. Hasselback the squid in the same way you did the potatoes.
Cut each corn cob into four pieces – the easiest way to do this is by positioning your knife, covering it with a tea towel and hitting it with a rolling pin. Add the corn to the tray, toss in the oil and return to the oven for 5 mins.
Mash together the butter, parsley, paprika, garlic and lemon zest. Stuff some of the butter into the back of each prawn and inside the squids. Turn the oven up to 220C/200C fan/gas 6. Add the seafood, lemon wedges and chorizo to the pan and toss everything together. Dot the remaining butter over the top, season well and return to the oven for 10 mins. If any of the prawns haven’t turned pink or any mussels haven’t opened, move them around the pan to the hot spots, then return to the oven for another 2-3 mins. Remove and discard any mussels which haven’t opened. Scatter some parsley over and serve.