1. Begin by leaving the cockles to stand in slightly salted water sprinkled with oatmeal overnight. This process enhances their flavor and texture.

2. The next day, drain the cockles and scrub them thoroughly to remove any grit or dirt.

3. Place the cleaned cockles in a saucepan of salted water and bring to a boil. Cook for 3 minutes, or until the shells open.

4. Once cooked, remove the cockles from their shells and set aside.

5. In a mixing bowl, rub the butter into the flour and add a pinch of salt for seasoning.

6. Separate the egg yolk and beat it lightly. Add the egg yolk and water to the flour mixture, and beat until a smooth batter forms.

7. Heat the cooking oil in a deep pan until hot.

8. Using a spoon, dip each cockle into the batter, ensuring it is fully coated, and then carefully drop it into the hot fat.

9. Fry the cockle cakes in the hot fat until they are golden brown and crisp all over, approximately 2 to 3 minutes.

10. Once cooked, remove the cockle cakes from the fat and drain them on paper towels to remove any excess oil.

11. Serve the Cockle Cakes immediately, accompanied by slices of brown bread and lemon wedges for a traditional Welsh treat.