Rinse the Dried Marrowfat Peas under cold running water and remove any debris or shriveled peas.
Place the peas in a large bowl and cover with plenty of Water. Stir in a pinch of Bicarbonate Of Soda to help soften the peas, then soak overnight (8–12 hours) or until plump.
Drain and rinse the soaked peas, then transfer to a heavy-bottomed saucepan and add fresh Water to cover by about 2–3 cm (1 inch).
Bring to a gentle boil, then reduce to a simmer. Cook uncovered, stirring occasionally and skimming any foam, until the peas are very tender and beginning to break down, 45–90 minutes depending on age of peas.
When the peas are tender, mash them gently with a potato masher or use a fork for a chunkier texture — or a hand blender for an ultra-smooth purée. Add a knob of Unsalted Butter and stir until melted and incorporated.
Season to taste with Salt, adjust butter or consistency with a little cooking liquid if needed, and serve hot alongside fried fish, roast meats, or on buttered toast.
