Add all the ingredients to a jar, top with the lid, and shake until the ingredients are completely mixed together. You can also add them to a small bowl and mix with a fork or a whisk until well combined.
Use it immediately or keep it in an airtight container in the fridge for 1 to 2 weeks. Shake before using. If your poppy seed dressing solidifies in the fridge, just let it rest at room temperature for 5 to 10 minutes.
Notes
Feel free to use any type of oil, vinegar, sweetener, or mustard you want to customize your poppy seed dressing recipe.