- In large skillet, melt 3½ tablespoons salted butter over low heat, and cook scallions and ginger until softened, about 7 minutes.
- Add peas and enough water to cover ingredients.
- Continue cooking over low heat until peas are just tender.
- In saucepan, melt unsalted butter with 1 cup water.
- Using electric mixer, beat to thicken and form emulsion.
- Pour emulsion over coriander leaves in mixing bowl.
- Mix with electric mixer and strain.
- Peel grapefruit, and cut into thin segments.
- Cut each segment of grapefruit in half.
- When peas are cooked, add remaining butter and season with sea salt.
- To serve, arrange alternating pieces of grapefruit with portion of peas, and spoon coriander sauce around perimeter.