Preheat the oven to 70 degrees and place four deep plates in the oven so that they are warm when ready to serve.
Peel the white asparagus thoroughly from top to bottom using a vegetable peeler. Cut the asparagus into bite-sized pieces.
Heat a pan with water, salt and butter, then add the white asparagus. Cover and steam the asparagus until tender for approx. 4 minutes. Remove the lid, toss the chives and chervil through the asparagus, then transfer to a sieve to drain off the liquid.
Chop the shallot and sauté it for about 4–5 minutes in the oil in a saucepan over a low heat, without letting it brown. Add the vinegar and reduce until only 2 tbsp of liquid remains. Add the white wine and reduce until there is about 100 ml of liquid left in the saucepan.
Now gently heat the liquid, without bringing it to the boil, and add the cold butter in small amounts at a time, whisking it into the sauce as you go. The heat can be turned up whilst the butter is being whisked into the sauce, but once all the butter has been incorporated, turn the heat down to the lowest setting. After this, the sauce must not be allowed to boil, otherwise it will separate.
Take a hand blender and blend the sauce thoroughly so that it thickens further and becomes light and airy, then season to taste with lemon juice, salt and pepper. Set the sauce aside and heat it gently just before serving, then blend it again.
Arrange the asparagus on the warm plates, spoon a few spoonfuls of the warm beurre blanc over the asparagus, and sprinkle with edible flowers and finely chopped chives. Serve immediately, ideally with some good sourdough bread on the side.
