Put the tray you are going to cook the fish on into the oven, then preheat the oven to 200°C. You want the tray to get hot, so leave it in there for 8 minutes. The reason for this is that you want to cook the brill at a high temperature to get a crispy skin but ensure that it still has juicy flesh.
Put 25ml of olive oil on to a chopping board and toss the fish in the oil, seasoning on both sides.
Take the hot tray out of the oven (remember, it is hot!), and place the fish on it with the dark skin on top. Return to the oven and cook for around 18–20 minutes.
While the fish is in the oven, pour the remaining 125ml of olive oil into a small saucepan and put on a medium heat. Add the garlic and cook until softened and pale gold. You don’t want it to crisp at all. Pour in the vinegar and lemon juice and whisk together – be careful when adding to the pan, as it will hiss. Add the paprika and chopped parsley and stir together.
When the fish is cooked, open the oven and pour over the dressing. Cook for another minute or so, then serve.