Heat olive oil or butter in a deep saucepan over medium heat. Add chopped onions and cook gently until soft and translucent, without browning. Stir in garlic and celery or leek if using. This aromatic base adds sweetness and depth, forming the foundation of the soup’s flavour.

Add diced potato to the pan and stir well to coat with the aromatics. Potatoes play a key role in creating body and creaminess without flour. Cook for a minute before adding liquid, allowing the starch to release gradually during simmering.

Pour in vegetable stock or water and bring to a gentle boil. Reduce heat and simmer until the potato pieces are completely soft and easily mashable. This step ensures the soup blends smoothly later, eliminating any graininess.

Add the chopped spinach to the pot and stir gently. Cover and cook just until wilted and bright green. Overcooking spinach can dull its colour and flavour, so keep this step brief. Turn off the heat once the leaves are fully wilted.

Add salt, black pepper and a pinch of nutmeg if using. Nutmeg enhances the natural earthiness of spinach without overpowering it. Keep seasoning restrained at this stage, as flavours intensify after blending.

Using a hand blender or countertop blender, blend the soup until completely smooth and velvety. Blend while warm to achieve the creamiest texture. If the soup feels too thick, add a splash of hot water or stock to adjust consistency.

Return the soup to low heat if needed. Stir in lemon juice to brighten flavours and balance the natural sweetness. Finish with a small drizzle of olive oil or butter for richness without heaviness.

Let the soup rest off the heat for a couple of minutes before serving. This allows flavours to settle and the texture to stabilise, giving the soup its signature creamy mouthfeel without any added cream.