Set up your immersion blender in a tall, narrow container. The key to perfect emulsification lies in using the right vessel – something just wide enough for your blender head creates the ideal vortex. Room temperature ingredients blend more easily, so let cold soy milk sit out for 10 minutes if needed.

Pour the soy milk into your container, followed by vinegar, lemon juice, mustard, salt, and garlic powder. These acidic ingredients help create the tangy flavor profile that makes mayo so irresistible. The mustard acts as a natural emulsifier, helping bind everything together.

Place your immersion blender at the bottom of the container. Begin blending while very slowly drizzling in the oil – this is crucial for proper emulsification. You'll hear the mixture change from liquid to thick as it transforms.

Continue blending while gradually moving the blender up and down. Watch as the mixture turns pale and creamy, doubling in volume. This process typically takes 2-3 minutes. You'll know it's ready when it coats the back of a spoon and holds its shape when dolloped.

Taste and adjust seasonings as needed. Add more lemon juice for brightness, salt for depth, or a pinch of sugar to balance acidity. The flavor should be tangy but not overpowering, with a rich mouthfeel.