Drain the soaked split peas and rinse under cold water. This helps remove excess starch and ensures a cleaner flavour. Transfer them into a large saucepan.

Place the peeled whole onion and bay leaf into the pan with the peas. Pour in enough fresh water to cover by at least 2 cm.

Bring the pot to the boil over medium heat. Skim off any foam that rises to the surface to keep the pudding smooth. Lower the heat and let it simmer gently.

Cook for 1 to 1½ hours, stirring occasionally, until the peas have completely softened and begun to break down. Add more hot water if the mixture becomes too dry.

Once the peas are tender, discard the onion and bay leaf. They will have imparted flavour but are not needed in the final mash.

Using a wooden spoon or potato masher, crush the peas into a thick, smooth paste. For a creamier pudding, you may also press through a sieve.

Stir in salt, pepper, and butter if using. Taste and adjust seasoning as needed. The butter adds depth, but traditional versions are often kept plain.

Return the pan to a low heat and stir for 5 to 10 minutes. This step dries the pudding slightly and improves its texture for spreading.

Allow the pudding to cool slightly. It will thicken as it rests, making it easier to slice or spread.

Spoon into a serving bowl or press into a dish to slice when firm. Serve warm or cold alongside boiled ham, bacon, or fresh bread. A dab of English mustard on the side makes a fine addition.