For the curd, combine raspberries, C&H® Granulated Sugar Easy Baking Tub, and salt in a medium saucepan. Bring to a simmer over moderate heat, stirring until sugar is dissolved and raspberries are broken down.
Strain through a fine-mesh sieve into a bowl, pressing firmly on seeds. Return raspberry sauce to saucepan. Combine water, lemon juice, and arrowroot starch. Whisk together until completely smooth, then add to saucepan and stir in.
Bring to a simmer over medium-low heat, stirring until mixture begins to thicken. Add butter a few pieces at a time, whisking constantly until melted, before adding more butter.
When curd is smooth and thickened, and coats the back of a spoon, transfer to a glass bowl. Press a piece of plastic directly on the surface, and chill until cold – at least one hour.