Step 1

In a medium mixing bowl, whisk together the egg yolk and the Dijon mustard until slightly thick and smooth.

Step 2

Slowly pour the oil in a very thin stream into the egg yolk mixture while whisking continuously with your other hand. The slower the better; starting off with a drop or two at a time isn’t too slow at all to achieve the best results. The mayonnaise will be very thick.

Step 3

Slowly whisk in the lemon juice until the mayonnaise is smooth, thick, and pale yellow in color.

Step 4

Season to taste with the cayenne pepper, the kosher salt, and the black pepper. Set it aside.

Step 5

Place the eggs in a medium saucepan and add the cold water, until the water reaches about 1-inch above the eggs.

Step 6

Cover the saucepan and place it over medium heat.

Step 7

Allow the water to come to a boil.

Step 8

Take the saucepan off the heat and let the eggs sit undisturbed until they reach your desired level of cooked, about 10-12 minutes.

Step 9

Set up a large bowl of ice water.

Step 10

Once the eggs have finished cooking, transfer them gently to the ice water using a slotted spoon.

Step 11

Allow the eggs to cool until they can easily be handled, about 5-10 minutes.

Step 12

Working one at a time, gently peel each of the eggs.

Step 13

Slice the eggs in half and transfer them to a medium mixing or serving bowl.

Step 14

Repeat until all the eggs are peeled.

Step 15

Add 1/2 cup of the homemade mayonnaise to the bowl.

Step 16

Gently mash the eggs and the mayonnaise together.

Step 17

Gently stir in the sliced chives.

Step 18

Season with the salt and the pepper.

Step 19

Place a small handful of the watercress on the bottom half of each slice of the bread.

Step 20

Top the watercress with the egg salad.

Step 21

Top the egg salad with more watercress and the top half of the bread.

Step 22

Serve.