To a blender, add one whole egg and one egg yolk. Use room-temperature eggs for the best results.
Add the garlic, lemon zest (if using), salt, and ~½ teaspoon of the oil into the blender with the eggs.
Begin blending on low speed and slowly stream in more oil while blending until you've added about three-quarters of the oil. Then, add the lemon juice.
Pause blending and scrape down the sides of the bowl. Evaluate the texture of the aioli. If the aioli is too thin, turn the blender back on and continue adding more oil (oil makes the aioli thicker). If the aioli gets too thick, you can add some extra lemon juice to thin it out. The final texture is up to personal preference!
Taste your finished aioli, and mix in more garlic or lemon zest if desired to suit your taste. Store finished aioli in an airtight container in the fridge and use within a few days of preparing.