Yes, you can make mayonnaise using only egg yolks. In fact, using just egg yolks instead of whole eggs can result in a richer and creamier texture. The egg yolks act as emulsifiers, helping to bind the oil and other ingredients together. When making mayonnaise with egg yolks only, the general ratio is one egg yolk per cup of oil. It's important to note that using only egg yolks may result in slightly thicker mayonnaise compared to using whole eggs.