Open out the leaves a little bit, run under water to clean. Trim a few inches from the petals (a bread knife can be useful for this), then trim the stem. Put upside down in a steamer placed over boiling water. Steam for 25-35 mins. It’s done when the knife goes through the stem easily or you can easily tear off a petal. Make sure there’s plenty of water in the pot... I’ve managed to boil mine dry a couple of times.
Then you’re ready to serve. Melt some butter and pour into a bowl. Tear off the petals one by one and dip into the butter. When you get to the very tender leaves you can either eat them or discard them (they don’t have much ‘meat’). Eventually you’ll get to the furry spiky part in the middle. Pull the spikes away or scrape them with a teaspoon. The part underneath is the heart which is delicious and you can also dip in the butter.
Brilliant thanks everyone! I might be back later when I actually tackle the thing I've made myself quite afraid of it. Is it more of a starter than a side? The eating sounds rather full on, we shall refer to your instructions at the dinner table @CloudsCloudsClouds
I second what everyone everyone else has said. Trim stem, steam until tender, then rip off leaves and dip in butter and then eat the heart when you get to it. They are delicious. When I lived in France I ate them literally everyday when in season.