Tip the egg yolks and mustard into a bowl, season with salt and pepper and whisk together until completely combined.

Whisking constantly, add a small drop of oil and whisk until completely combined, then add another drop and continue a drop at a time until the yolks and oil combine and start to thicken.

Once you’re confident the oil and eggs are coming together you can add the oil a bit more at a time, but be patient, as adding the oil too quickly will cause the mayonnaise to split and curdle.

Once all the oil has been whisked into the eggs and you have a thick, spoonable mayonnaise, whisk in the vinegar or lemon juice and season to taste. Will keep in the fridge for two days.