How to balance out sourness of lemon juice, specifically in a mayonnaise?

To balance acidity, add sugar. It's how most mayonnaise manages to be acidic enough to prevent bacteria growth (pH 4.6 or lower), while still having a balanced and edible flavor.

You might get an edible result with honey, but sugar is more of a neutral flavor, so I would use that first. Using a jigger of Dijon mustard is not beyond the pale, as well... might help hide the acid, to a lesser extent.

The last time i made lemon chicken it turned out too sour, so i added a bit of baking soda and stirred until the fizz was gone. I tested and added a bit more. It was perfect. Very lemony but not sour. I heard adding too much baking soda can leave a weird taste but i guess i didn't add enough to have that problem. Just my two cents, good luck!

As a chef of 6 years now working at a high level requirement in hotels around the country I will give you this tip: adding water will cut down the flavor so I suggest to avoid watering down a dish, sugar is a balancing technique we use to balance out most of our sauces, and I will explain why this works.

When a person's palate tastes sugar immediately the brain picks it up, you may not notice it but think about it the next time you have a coffee with 1-2 sugars, or ask a friend to make 3-4 drinks add sugar to one of them. The taste buds react with sugar/water in the mouth which sends a message to the brain "this is sugar". Not everyone likes a super sweet sauce so I suggest adding a small amount at a time and Taste, depending on how much lemon you have used you can cut it down a spoon at a time.

I have used sugar or, on occasion, honey, though I usually mix it in at the start, before I've started adding oil. It works fairly well. Personally, I prefer an acidic mayonnaise, but some applications call for a sweeter one, so I certainly don't think there's anything wrong with adding a bit of sweetener.

Additionally, you might succeed in taking the edge off with some contrasting flavors. I usually have a little mustard in my mayonnaise, partially for the emulsifying effect, but also for flavor. Some spanish paprika blended in may soften the acidity as well.

You can get a less sharp-tasting mayonnaise by using a vinegar instead of lemon juice, or slightly diluted lemon juice. Each vinegar has its own properties, so there's plenty of room for experimentation. I've usually used cider vinegar or rice vinegar, but occasionally I've started with an aromatic fruit vinegar.

I used sugar. Depending on what your making, a dash of parm cheese works. I used parm cheese for chicken picatta when I added to much lemon.

You can add more oil and/or cut it with water. Mayonnaise is a very flexible emulsion once set -- if it's too tart, you can add more oil and then cut it with water to manage thickness. You can then adjust salt/pepper as necessary.