Heat your oven to 180°C/Fan 160°C/Gas 4. Scrub the potatoes and cut them so they’re all roughly the same size, keeping as many as possible whole.
Pop the potatoes in a pan and cover with cold water and a pinch of salt. Bring to the boil, cover and simmer for 10-15 mins till the potatoes are tender. Peel and slice the chioggia beetroot as thinly as possible.
Drain the potatoes. Add them to a roasting tin. Drizzle with ½ tbsp oil and seasoning. Add the beetroot. Toss together. Cook in the oven for 20 mins.
Peel and thinly slice the shallot. Zest and juice the orange and lemon.
Heat a third of the butter in a large frying pan with 1 tsp oil. Add the cod, skin-side down. Cook for 2 mins. Pour in the orange juice and zest and 1 tbsp of the lemon juice. Bring to a simmer then add the remaining butter and plenty of freshly ground pepper. Put on a lid and cook for 5 mins.
Carefully lift out the cod with a fish slice or spatula and place on a plate. Pour the orangey butter into a small jug. Cover both with foil.
Using the same pan, add the shallot and fennel seeds with a pinch of salt. You shouldn’t need to add any more oil. Cook on a high heat for 2 mins then add the spinach with the lemon zest and remaining juice. Stir till the spinach is wilted.
Serve the cod fillets with the roasted veg and the wilted spinach. Pour over the orange butter sauce. Scatter over the edible flowers.