From Chow Bella
1 1/4 cups light olive oil, divided
1 egg, at room temperature (or place in a cup of hot water for about 15 min)
1/2 tsp mustard powder
1/2 tsp salt
generous dash of cayenne pepper
1/4 tsp (half a small) garlic clove, grated
juice of 1 lemon
1/2 tsp dried tarragon (or about 1 tbsp fresh tarragon, minced)
1. Add 1/4 cup of the olive, the egg, mustard powder, salt, cayenne, and garlic to the cup that comes with the immersion blender (or food processor bowl, blender base, etc...). Blend until bubbles form.
2. Drizzle in the remaining oil very slowly in a thin stream. If it gets to the point that the mayo is thick enough that the oil starts pooling on top, just keep moving the immersion blender until it is incorporated before proceeding.
3. Once the mixture is emulsified, stir in the lemon juice and tarragon with a spoon.