Lamb's lettuce does not need to be washed like wild herbs — as a cultivated vegetable from the store, it comes already cleaned. Still, rinse it briefly under running water to remove grains of sand from the leaf rosettes. The leaves are very tender and need no preparation — straight into the container.
Do not peel the apple: the skin contains fiber and gives the smoothie some structure. Cut the apple roughly into pieces (remove the core to taste). The banana should be ripe to overripe — yellow with brown spots — which provides the sweetness needed and a creamy texture without sugar.
Lamb's lettuce has a short season (October to March), but it is available year-round as organic produce. In winter it is particularly inexpensive — that is when the smoothie pays off most. If you cannot get it fresh, you can replace it with young arugula or leaf spinach, but then expect more sharpness or some oxalic acid.
Lamb's lettuce is tender, but its small leaf rosettes hold grains of sand and fine fibers that weaker machines leave behind as a slightly grainy texture. Your Vitamix fully breaks down even tender leaves — the result is silky, uniform green with no grain in the glass. The speed ramp (low to high) also ensures that the light leaves are caught by the vortex first, before the highest setting finalizes the texture.
You will also find this smoothie in our overview of green smoothies.