In a mixing bowl, combine the chia seeds, milk, sweetener, and vanilla extract (if using).
Whisk the mixture together until the chia seeds are evenly distributed and there are no clumps.
Let the mixture sit for a few minutes, then whisk again to prevent clumping.
Cover the bowl and refrigerate for at least 2-4 hours or overnight to allow the chia seeds to thicken and absorb the liquid. Stir or shake the mixture once or twice during the setting time to ensure even consistency.
Once the chia pudding has set and reached your desired consistency (it should be thick and pudding-like), give it a good stir.
Divide the chia pudding into serving jars or bowls.
Serve chilled, topped with your favorite toppings such as fresh fruit, nuts, seeds, granola, or shredded coconut.
Enjoy your delicious and nutritious chia seed pudding!