Whisk Greek yogurt, milk, maple syrup, vanilla, cinnamon and salt for 45 to 60 seconds until smooth and pourable.
Whisk continuously while sprinkling chia seeds slowly and widely over the surface instead of dumping them in one spot.
Rest 5 minutes, then whisk thoroughly and scrape the bottom, pressing apart any small clusters.
Rest 10 more minutes and stir again; the mixture should be thicker but still pourable.
Divide among four clean containers, cover immediately and refrigerate at 40°F or below for at least 4 hours.
Stir from the bottom, add milk 1 tablespoon at a time if too firm, and top with berries and optional nuts.
