In a small bowl, whisk the tahini with 1 tablespoon water. The tahini will become thick and heavy. Continue adding the water 1 tablespoon at a time, whisking after each addition until the tahini is smooth and light.
Add the lemon juice, olive oil, maple syrup, salt, and Dijon mustard. Whisk until everything is blended and the dressing drizzles off the whisk easily. Taste and adjust seasonings if needed. Use immediately or store in the refigerator in a jar or other airtight container for up to one week.