Mustard.

Judicous amounts of sharp cheese. The most regal Egg Mayo binlid I ever had contained Parmesan. Also swap the cress out with Spinach or Rocket.

>>13324
Definitely.

Also, my mum used to make them with salad cream as we couldn't afford mayonnaise.

Lashings of butter and really good quality bread. If you want to get fancy, make your own mayonnaise. The core flavours are all very subtle so you don't want to drown them out, but I think a slightly more acidic mayonnaise cuts through the fat, perhaps with a tarragon vinegar. I'm not wholly opposed to mustard, but I'd go with Dijon over English.

Lemon juice, dijon mustard, chilli flakes.

Use quality mayo. Heinz / Hellman’s etc are trash.I can recommend Stokes for all your saucy needs.

There's nothing fancy about making your own damn mayonnaise. It's just egg yolk in a pint of oil. Making your own takes about as much time and effort* as remembering to buy a jar and it's even cheaper. You can add all those other things in too.

*Slightly more if you don't have an electric whisk or food processor.

>>13329
Polish 'majo' is way better than the shite over this side of Europe anyway. Get yourself some of the Winiary stuff in your world foods aisle. That said, it's probably because it comes with mustard already in it.

>>13331
I often find the world section has decent alternatives to well known brands but I wonder if the standards are there. GMOs, animal welfare, etc.
The logo looks suspiciously like Maggi's, but according to wikipedia they're unrelated.

>>13332

>>13332
>The logo looks suspiciously like Maggi's
Is your name Dominic Cummings?

Japanese mayonnaise is really quite spectacular, Kewpie is the brand you'll most likey find over here.

It goes without saying that better eggs and bread will also help your sarnie along. The former perhaps not as important once smothered in mayo.