Serves: 4 people. Preparation time: 20 minutes.
For the dressing, strain the grapefruit juice if necessary, into a large bowl and add the vinegar and mustard. Add the olive oil in a slow stream, continuously whisking to emulsify. Add salt to taste and store in the refrigerator to thicken. Peel, section and chill the grapefruit too.
Peel and devein the shrimp. To cook the shrimp, bring a pot of salted water to a boil. Have a bowl of ice water at the ready. Add all the shrimp to the boiling water and cook for about 1 minute. Cooking time will depend on the size of the shrimp. Remove the shrimp from the boiling water as soon as they are cooked and immediately place them in the salted ice water. When completely cool, quickly remove the shrimp from the water to prevent oversaturation. Pat dry.
To serve, marinate the shrimp in the cold grapefruit dressing for a few minutes. Arrange 5 shrimp on a salad plate. Spoon more dressing on top and add 2-3 grapefruit segments per serving. Dust with paprika and sprinkle with freshly ground pepper and sea salt. Serve immediately.