Mayo is an emulsion of ingredients that don't naturally meld. It’s made by mixing oil and the water from egg yolks and vinegar with the help of the yolks’ lecithin — an emulsifier.

However, a few factors can cause the sauce to separate into a curdled mess with pools of oil floating on the top. Thankfully, re-emulsifying the broken mayo can solve the issue.

You can do that by taking an extra egg yolk in a separate bowl and whisking in the broken mayo little by little until it thickens and regains its homogeneous appearance.

Alternatively, slowly whisk spoonfuls of your separated mayo with a teaspoon of mustard sauce until it begins to emulsify. Then, add the remaining separated mayo to the mixture.

For better emulsification, whisk the broken mayo with both an extra egg yolk and a little mustard. Or, add a teaspoon or two of boiling water directly into the separated condiment.

If excess oil is still an issue, beating the mayo with lemon juice or vinegar can help. Use a room-temperature yolk if your mayo is runny or refuses to emulsify due to being cold.