Trim and scrub the carrots. Roughly chop them (no need to peel unless you want to). Quarter the apple. Slice out the core and seeds, then roughly chop the apple (again, no need to peel). Pop them all in your blender.
Peel the bananas and chop them. Tip the bananas into the blender. Add the kefir and walnuts. Grate in ¼ of the nutmeg. Blend till smooth with a handful of ice cubes. Taste and add a little more nutmeg if you like. Serve straight away.
The big freeze
If you have time, pop the bananas in the freezer for 4-8 hours. This will give you a cooler, creamier smoothie.