Trim the leeks and remove dark green tops, cleaning thoroughly to remove grit. Thinly slice leeks and shallots.
Lightly crush coriander seeds using a mortar and pestle.
Warm a wide saucepan or deep frying pan over medium heat. Add the olive oil and butter and let it melt gently.
Add the sliced shallots and cook for about a minute until they soften in the butter.
Add the sliced leeks in batches, stirring to coat them well. Cook for 5 minutes, keeping the heat medium, allowing the leeks to soften but not colour.
Season with a pinch of salt, crushed coriander seeds and black pepper. Stir to combine.
Pour in the cider. Let it bubble briefly, then reduce the heat to low and simmer gently for 15–20 minutes, stirring occasionally.
The leeks should slowly collapse and soften. If after 20 minutes there is still noticeable liquid in the pan, continue cooking for another 5–7 minutes.
The goal is very well-cooked leeks with almost no liquid remaining - they should taste sweet and melt in the mouth.
When the leeks are fully cooked and the pan is nearly dry, add the cream (or more if you like it richer). Stir through and cook for another 3–4 minutes until the cream lightly hugs the leeks without creating a runny sauce.
Taste and adjust seasoning.
Serve warm as a bed for grilled or pan-fried salmon, or alongside any delicate white fish.
