1 1/4 cups light olive oil (NOT extra-virgin), divided
1/2 teaspoon mustard powder
1/2 teaspoon salt
1/2 to 1 lemon, juiced
Place the egg, 1/4 cup olive oil, mustard powder, and salt in a mixing bowl, blender, or food processor. Mix thoroughly.
While the food processor or blender is running, slowly drizzle in the remaining cup olive oil.
After you’ve added all the oil and the mixture has emulsified, add lemon juice to taste, stirring gently with a spoon to incorporate.