Heat the olive oil in a large frying pan, add the mushrooms, along with the garlic and cook for a couple of minutes over a medium heat – shaking the pan and stirring from time to time.
Now pour in the red wine, turn the heat up higher and let it all bubble for a minute or two and reduce a little. Turn the heat down and cook for a further 4 minutes. Season to taste, stir in the chopped parsley and then transfer to a small serving dish. Allow the mushrooms to cool before covering them and popping them into the fridge to chill.
Now make the mayonnaise. First, place a medium-sized mixing bowl on a damp tea cloth so it will remain steady and leave you both hands free to make the mayonnaise – one to drip the oil, the other to hold an electric hand whisk. Next, measure out the oil into a jug. Now put the egg yolks into the bowl, adding the garlic, mustard powder, salt and a little freshly milled black pepper and mix all of these together well. Then, holding the jug of oil in one hand and the whisk in the other, add just a drop of oil to the egg mixture and whisk this in. However, stupid it may sound, the key to a successful mayonnaise is making sure each drop of oil is thoroughly whisked in before adding the next drop. It won't take all day, because after a few minutes – once you've added several drops of oil, the mixture will begin to thicken and go very stiff and lumpy. When it gets to this stage, you need to add the vinegar, which will thin it.
Now the critical point has passed, you can begin pouring the oil in large drops, keeping the whisk going all the time. When all the oil has been added, taste and add more salt and freshly milled black pepper, if it needs it. If you'd like the mayonnaise to be a bit lighter, add 2 tablespoons of boiling water and whisk it in. You can also watch How to Make Mayonnaise in the Cookery School Video on this page. Finally, stir the smoked, sweet pimentón into the finished mayonnaise.Serve the mushrooms on crisp lettuce leaves with some chopped parsley sprinkled on top, and about a dessertspoon of mayonnaise per person.
The leftover mayonnaise will keep for a week in the fridge.
Note: Mayonnaise only curdles when you add the oil too quickly at the beginning. If that happens, don't despair. All you need to do is put a fresh egg yolk into a clean basin, add the curdled mixture drop by drop, then continue adding the rest of the oil as though nothing had happened. This recipe contains raw eggs.