Measure and add the dry mustard, salt, paprika, and sugar to a clean jar with a tight-fitting lid or to a medium bowl.

Add the lemon juice. Stir with a spoon (if using a bowl) or close the jar and shake until the sugar is dissolved and the mixture is uniform.

Add the oil. If using a bowl, slowly drizzle the oil in while whisking constantly until the dressing becomes smooth and combined. If using the jar, pour in the oil, secure the lid, and shake vigorously until the dressing is well emulsified.

Taste and use immediately, or transfer to the refrigerator.

Refrigerate any leftovers and shake or whisk briefly before serving, as the oil may separate.