Bring a large pot (with a lid) of water to a boil, and add a few handfuls of salt until the water tastes salty.
Slice the chard leaves and trim the brownish ends from the stems, and cut the stems into 1- or 2-inch-long pieces. Add the stems to the boiling water, and stir occasionally until they’re tender but still have a little crunch (about 2 minutes).
Add the chard leaves to the pot, stir well to make sure they’re all submerged, and pop on the lid. Return the water to a boil, remove the lid, and cook, stirring occasionally, until the stems have just lost their crunch and the leaves are tender and silky. (This should take 6 to 8 minutes from the moment you add the chard leaves.)
Drain the chard well in a colander, but try not to squeeze it too much. Put it in a bowl, drizzling on the olive oil and adding the garlic. Toss together with your hands, rubbing the leaves to make sure the garlic is dispersed.
Squeeze just a bit of lemon juice for brightness, and sprinkle on some Maldon salt.
Lay the chard on the plate in an airy tangle—not a dense clump—and serve.