Place the basil, parsley, cilantro, dill and oregano in the food processor and pulse to chop. Add the mayonnaise and pulse several times to blend. Pulse in the egg yolk, lemon juice, salt and several grinds of pepper. With the motor running, very slowly drizzle in the olive oil through the feed tube on top or with a slow and steady hand until the mixture is completely incorporated and —if things went well—somewhat fluffy. Scrap down the sides and blend again. Taste and adjust the seasoning as needed.