Preheat your oven to 220°C/200°C fan/gas mark 7. Put a large saucepan of water with 1/2 tsp salt on to boil for the potatoes.
Chop the potatoes into 2cm chunks (peel first if you prefer).
Halve any large broccoli stems lengthways. Halve, peel and thinly slice the shallot. Peel and grate the garlic (or use a garlic press).

When your pan of water is boiling, add the potatoes and cook until you can easily slip a knife through, 15-20 mins.
Meanwhile, pop the broccoli on a baking tray. Drizzle with oil, season with salt and pepper, then toss to coat. Set aside for now.

Meanwhile, pop the breadcrumbs, pesto and olive oil for the crumb (see ingredients for amount) into a small bowl and mix together.

Lay the sea bass, skin-side down, onto a lined baking tray. Spoon the pesto crumb evenly over the fish, pressing it down with the back of the spoon.
Pop the broccoli on the top shelf and the sea bass on the middle shelf of your oven to roast until the broccoli is tender and the fish is cooked through, 12-15 mins. IMPORTANT: Wash your hands and equipment after handling raw fish. The fish is cooked when opaque in the middle.

Heat a drizzle of oil in a medium frying pan on medium heat. Once hot, add the shallot and stir-fry until softened, 3-4 mins.
Stir in the garlic and cook for 1 min. Add the cider vinegar and allow it to evaporate, 1-2 mins.
Pour in the water for the sauce (see ingredients for amount) and vegetable stock paste, then bring to the boil and simmer until reduced by half, 2-3 mins. Vigorously stir in the butter until melted, then take off the heat.

Once the potatoes are cooked, drain in a colander and return to the pan, off the heat.
Add a knob of butter and a splash of milk (if you have any) and mash until smooth. Season to taste with salt and pepper.
Serve the fish with the mash and roasted broccoli alongside, then spoon over the sauce. Enjoy!