Step 1

Put the marrowfat peas and bicarbonate of soda in a large heatproof bowl and cover with boiling water. Leave to soak for 12 hours or overnight.

Step 2

Drain the peas and rinse them twice with cold water to wash off the bicarbonate of soda. Put the beans in a saucepan and cover with 650ml cold water. Bring to the boil, reduce the heat and simmer for 30 mins until tender, stirring occasionally.

Step 3

Mash briefly and stir in the butter, mint and lemon, seasoning to taste.