1 large egg yolk
1 1/2 teaspoons fresh lemon juice
1 teaspoon white wine vinegar
1/4 teaspoon Dijon mustard
1/2 teaspoon salt plus more to taste
3/4 cup extra virgin olive oil, divided in half
1 tablespoon fresh rosemary minced
Combine egg yolk, lemon juice, vinegar, mustard, and 1/2 teaspoon salt in medium bowl. Whisk until blended and bright yellow, about 30 seconds.
Using 1/4 teaspoon measure and whisking constantly, add 1/4 cup oil to yolk mixture, a few drops at a time, about 4 minutes. Gradually add remaining 1/2 cup oil in very slow thin stream, whisking constantly, until mayonnaise is thick, about 8 minutes (mayonnaise will be lighter in color). Fold in Rosemary. Cover and keep chilled.