Whisk egg yolks in a bowl. Continue to whisk and pour in oil in a very slow trickle, until it has all been absorbed. Still whisking, add salt, pepper and lemon juice to taste. Stir through basil, parsley and nuts to give a smooth very thick sauce. If the mayonnaise appears to be curdling, continue its preparation to the finish.
Beat another egg yolk in a clean bowl and gradually whisk in the curdled sauce. The mayonnaise will keep, covered and chilled, for up to 24 hours. This is delicious served over hot fresh herb fettuccine or with cold shellfish and sugar snap peas in a pasta salad. It is less successful if made with a food processor of blender.