Zest the lime. Sprinkle it with the kosher salt, then mince it as fine as possible. Holding the blunt edge of the knife, scrape the sharp edge of the blade over the minced lime zest, holding the knife at an angle and mashing the zest into a paste. This should only take a minute or so: don’t spend too long on it!
Place the zest in a medium bowl and it whisk together with the Dijon mustard, lime juice, and maple syrup. Gradually whisk in the olive oil 1 tablespoon at a time (8 tablespoons total), until creamy and emulsified.
Taste and if desired, season with additional salt (if the dressing tastes too tart, add a pinch of sugar or a bit of honey). Store refrigerated for up to 2 weeks; bring to room temperature before serving.