Puree together the fresh banana and the kefir until combined. Then, add the frozen banana, maple syrup, and greek yogurt. Blend for at least a minute until fully combined. The ice cream base should be creamy, and thick.
Reserve 2/3 of the banana nice cream base and transfer it into a large bowl. Add the frozen blueberries to the blender and puree with the 1/3 of the banana nice cream base. Blend until the ice cream is one solid purple color.
Add large spoonfuls of the banana ice cream base and the blueberry base to a glass casserole dish (mine was 9x9 inches). Once the bottom of the dish is covered, use the back of a large spoon to marble together the different colors of ice cream. If you're uncertain, please look at the photos in the blog article above.
Once that layer is done, continue adding the rest of the banana base and the blueberry base until all of it is in the casserole dish. Repeat the marbling process and freeze overnight.
When you are ready to enjoy, take the ice cream out. I recommend letting it sit at room temperature for 15-20 minutes so it is easier to scoop. Scoop the ice cream, top with frozen blueberries, and serve.
Happy cooking!! Enjoy