Take a soft brioche bun, split and toasted on the cut side. Flake 120g of hot smoked mackerel — line-caught if you can — and warm it gently in a pan with a teaspoon of butter.
Dress the bottom bun with a teaspoon of crème fraîche and a few leaves of watercress. Pile the fish on top, finish with a squeeze of lemon and a turn of black pepper, and put the top bun on.
Eat at the window seat. The roll is on the breakfast menu from six and the lunch menu from twelve.