Step 1
Make sure your butter is kept in the fridge until ready to add to the beurre blanc. If the butter gets to room temperature, the sauce is more likely to break, so keep it cold until you need it.
Step 2
Pat the seabass skin dry with a paper towel and sprinkle salt over both sides, patting it in. Set aside. Everything will come together quite quickly from now on, so the following steps may need to be done simultaneously. If you aren’t confident multi-tasking, you can cook the asparagus and fish first, set them aside off the heat (keeping them in the pan to retain heat), then make the sauce separately.
Step 3
Start by dry-frying the asparagus to bring out a nutty flavour. In a frying pan (preferably one with a lid) over a medium-high heat with no oil, fry the asparagus for a few minutes, flipping until starting to char. Sprinkle a little salt while cooking. When starting to blister and colour, add 2 tablespoons of water to the pan and cover with the lid (you can use a lid from another pan if you don’t have one that fits exactly, or a plate will also work if you are very careful to protect your hands from the heat when lifting it off). Steam for 2 minutes, or until the water has all evaporated.
Step 4
While the asparagus is steaming, add the olive oil to another large frying pan over medium-high heat. Once hot, add your sea bass fillets, skin-side down. Fry for 3-5 minutes, ideally pressing down gently with a spatula to increase contact with the pan. You can carefully lift the sides of the fish to check on it - look for crisp, browned skin. If it looks like it is burning then turn the heat down. Flip the fish and cook for another 2 minutes on the other side.
Step 5
While the fish and asparagus are finishing cooking, you can make the beurre blanc. Add the vinegar, wine and shallot into a small saucepan and bring to a gentle simmer, on medium-high heat. Simmer, swirling the pan regularly so as not to burn, until there is about 1 tablespoon of liquid left.
Step 6
Add the cold butter one chunk at a time, while whisking constantly with a whisk. Once the first chunk of butter is almost fully melted, add the next, and repeat until all the butter is melted, whisking the whole time to emulsify. The sauce should be thick, glossy and pale yellow. Remove from the heat. You probably won't need to season the sauce as the butter is salted, but taste it to check. The sauce can split easily if it gets too cool or too hot, so serve immediately over the fish and asparagus.
