Step 1

Put the split green peas in a large pot with the baking soda and enough water to cover the peas four times over. Cover and allow to rehydrate in the fridge overnight.

Step 2

Drain the peas in a colander and rinse with cold water to remove any lingering baking soda.

Step 3

Return the peas to the pan and cover with cold water by 1/2-inch. Add some salt, bring to a boil and then reduce the heat to a simmer. During the simmering, discard any pea foam that forms on top using a slotted spoon. The peas are done cooking once they just lose their bite, 30 to 40 minutes. Overcooking results in soup, which isn't what we're going for.

Step 4

Remove from the heat, add the butter and stir to fully incorporate. Taste and add more salt if required.

Step 5

Serve immediately with fish and chips, or cool and store for up to 3 days.