In a large bowl, whisk the first six ingredients. Cut in butter until mixture resembles coarse crumbs. Add rhubarb; toss to coat.
Measure the cream into a 1 cup liquid measure,add the egg, and vanilla; stir to combine. Add into crumb mixture and stir just until moistened.
Turn onto a floured surface; fold over gently 4-5 times. Pat into an 8-inch circle. Cut into eight wedges. Place wedges on parchment paper-lined baking sheet; sprinkle with sparkle sugar.
Bake 20-25 minutes or until light golden brown. Serve warm with Rhubarb Ginger Marmalade.