Place the blackberries in a bowl. Mash with a fork. Add the sweetener. Stir to combine. Add the 1/2 teaspoon chia seeds. Stir to combine. Set aside.
In a food processor or blender, add the plant-based milk and banana. Pulse until smooth. Add 1 teaspoon of sweetener. Pulse again to combine. Add the chia seeds and vanilla. Pulse one more time. Pour into a lidded container.
Cover and refrigerate at least 45 minutes to an hour, or overnight. It will thicken more the longer it sits, so if you prefer a firmer pudding, refrigerate overnight.
When you're ready to serve, pour equal amounts into two serving dishes. Top with equal amounts of blackberry sauce. Add almond slivers, granola or coconut flakes for garnish.
* I prefer maple syrup, agave, or honey. You can also use stevia in the same quantities.