Place the potatoes and the kosher salt in an 8-quart pot and fill it with enough water to cover the potatoes. Bring the water to a gentle boil and cook the potatoes until tender. Drain. Peel the potatoes while they are still warm and slice them 1/2-inch thick.
Whisk together the mayonnaise, evaporated milk, vinegar, mustard, and sugar in a small bowl. In a large bowl, combine 1/3 of the potatoes, eggs, onion, and celery with about 1/3 of the mayonnaise mixture. Repeat with the remaining ingredients, combining them 1/3 at a time until they are well mixed. Season with salt and pepper. Refrigerate for 1 hour, then garnish with paprika and chives.
Whisk together the egg yolk, mustard, and lemon juice in a large stainless-steel bowl. Add a few drops of the oil and continue whisking. Gradually add the oil in a thin stream while continuing to whisk. Stop every few seconds and check that all the oil has been incorporated. Season with the cayenne and salt and pepper. Store in the refrigerator for up to 2 weeks.
Yield: 1 1/2 cups
*RAW EGG WARNING
Food Network Kitchens suggest caution in consuming raw and lightly-cooked eggs due to the slight risk of Salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly-refrigerated, clean, grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell.