The Asparagus: Prepare the asparagus spears by bending the stems until they snap, then discarding the woody ends. Then, using a small knife, remove the "scales" on the remaining stems so they are smooth. Put a saucepan over a high heat, add the olive oil and saute the asparagus all over, without letting it color too much. Add the vegetable stock and the mint leaves. Cook for another 3-4 minutes (the asparagus should still be slightly crunchy). Drain over a bowl, reserving the cooking liquid, then chill the asparagus in the fridge. Remove the mint from the cooking liquid.
The Hollandaise Sauce: Melt the butter over a gentle heat, then remove from the heat. Using a spoon, skim the foam from the top, then pour off the yellow clarified butter and discard the white milk solids that will have separated out. In a saucepan, whisk together the egg yolks, the 2 Tablespoons asparagus-cooking liquid and a pinch of salt. Place over the lowest heat possible and whisk rapidly for 3-4 minutes. As soon as the sabayon is good and foamy, remove from heat and gradually mix in the warm clarified butter. Finally, stir in the lemon juice and finely chopped mint. Check the seasoning.
Finishing off and plating up: Heat oven to 300 degrees F. Put the asparagus in a baking dish, cover with damp kitchen paper and reheat for 2 minutes. Divide between 4 plates. Using a pastry brush, coat the asparagus spears with a little olive oil to make them glossy, then scatter over the fleur de sel and a few mint leaves. Serve immediately with the hollandaise sauce.
Recipe by The Culinary Cellar at https://theculinarycellar.com/scook-the-complete-cookery-course/