Step 1 Place the yolk in a stainless steel bowl. Begin whisking in the grape seed oil drop by drop. Once the mixture has thickened and emulsified, whisk in the remaining grape seed oil and the olive oil in a slow, steady stream. If the mixture gets too thick, add a drop or two of water.
Step 2 With a mortar and pestle, pound the garlic with one-third teaspoon salt. Whisk the garlic paste into the aioli. Season with one-fourth teaspoon salt, a squeeze of lemon juice, the lemon zest and cayenne. Taste for balance and seasoning. If the aioli seems thick and gloppy, thin it with a little water until creamy.