Serve one teaspoon mayonnaise on top of chilled clams on the half shell.
For variations, add 1 tablespoon of any of the following ingredients: roasted garlic, basil chiffonade, chopped chipotle peppers, finely diced roasted red peppers, or prepared horseradish to one cup of mayonnaise.
In a bowl, combine lemon juice and champagne vinegar.
In a separate glass bowl, whisk together egg yolk and dry ingredients.
Add half of the lemon juice mixture to the dry ingredients. Mix well before adding any oil. Begin adding oil, a little at a time, until it is incorporated into the emulsion. The color should lighten once 1/4 of the oil is emulsified. Then add the oil in a slow constant stream, whisking continuously. After 3/4 of the oil is incorporated, add the rest of the lemon juice mixture.
Continue to whisk until all of the oil is incorporated. Leave at room temperature for 1 hour. Refrigerate, covered, for up to 1 week.
*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.