Soak saffron in vermouth for 3 minutes and stir in citrus zests and orange juice.
Beat the butter with garlic, chives, sumac, cumin, and seasoning until reaching a smooth consistency.
Roll the butter in cling film into a sausage shape and chill for two hours until firm.
Boil swede in salted water for 20 minutes until tender and drain well.
Blend swede until smooth and mix with tahini, garlic, cumin, lemon juice, and olive oil.
Fry langoustines in olive oil for 2 minutes until pink and cooked through.
Melt 75g of the flavored butter in the warm pan off the heat.
Serve langoustines drizzled with melted butter, topped with butter slices, alongside mash and salad.