Blender Prep: Add all the ingredients except the poppy seeds to a medium bowl or canning jar. Use an immersion blender to blend all the ingredients together until smooth. Stir in the poppy seeds until well combined. (Do not blitz the dressing once the seeds are added.)Manual Prep: In a medium bowl, whisk all ingredients except milk together until smooth.For thinner dressing: Add a little milk when you blend ingredients.For thicker dressing: Blend ⅛ teaspoon xanthan gum into the mixture.It is important to thoroughly blend the xanthan gum into the mixture; don't just stir it in with a spoon. Xanthan gum does not work immediately; the dressing will set up in the fridge after in 30 minutes to an hour.
Taste and adjust seasonings to taste. Transfer dressing to a clean jar with a lid.
Refrigerate at least 30 minutes to allow the dressing to set up. Shake well before using.