Start by grating the sweet onion using a fine microplane until it becomes almost like a smooth pulp. This releases natural juices and sweetness that blend evenly into the vinaigrette without leaving strong chunks or harsh onion bites.

In a bowl or jar, combine grated onion, Dijon mustard, honey, apple cider vinegar, and lemon juice. Whisk everything together until smooth and fully blended into a tangy, slightly sweet base with a strong aroma.

Add finely minced or grated garlic into the mixture. Stir well so the garlic spreads evenly through the dressing. It should add a mild savory depth without overpowering the sweet onion flavor in the vinaigrette.

Add salt, black pepper, and celery seed if using. Stir well and taste the mixture before adding oil. Adjust sweetness or salt at this stage so the flavor base is balanced and ready for emulsification.

Slowly pour olive oil into the mixture while whisking constantly. This gradual process helps emulsify the dressing, creating a smooth, slightly thick texture that holds together instead of separating into layers of oil and vinegar.

Taste the vinaigrette and adjust flavors as needed. Add a little honey for more sweetness, extra vinegar for tang, or more olive oil for smoothness. This step ensures the dressing matches your personal flavor preference perfectly.

Transfer the finished vinaigrette into a clean jar or bottle. Let it rest for at least 15 minutes before serving so flavors meld together. Shake well before each use as natural separation may occur over time.