1. Add egg, mustard, vinegar, lemon juice and salt to a tall, narrow jar; pour oil over top. 
2. Pressing an immersion blender firmly against the bottom of the jar, blend on high speed until a creamy white mixture begins to form at the bottom (15-30 sec.). 
3. Slowly lift the blender up and down to emulsify the oil until mixture is fully homogeneous and thick. 
4. Add additional salt or vinegar to taste.

Tasty Tips:

• Sometimes called a stick blender, an immersion blender will yield the best results with this recipe. If you don’t have one, you can use a small (not full-size) food processor instead: Process egg for 20 sec. Add mustard, vinegar, lemon juice and salt; process for another 20 sec., then scrape the bowl. With the processor running, drizzle in about ¼ cup oil as slowly as possible until mixture begins to thicken. Stream in remaining oil, still quite slowly, until all oil is added. Scrape the bowl again; process for 20 sec. more or until done. Season as noted above.
• White wine vinegar may be used in place of the red wine vinegar, if desired.
• Mild olive oil can also be used, if desired.