Put basil, garlic, olive oil, pine nuts, and salt in a blender. Puree until smooth. Transfer to a bowl and chill. Slowly blend in the cheeses by hand or with a spoon. When everything is well blended, add the softened butter.
Steam the shrimp for about 5 minutes. Transfer the shrimp to an ice bath or refrigerate until chilled. Arrange shrimp on a platter and spoon pesto on top of each piece.