Preheat oven to 400°. In a large bowl, whisk the first 6 ingredients. Cut in butter until mixture resembles coarse crumbs. Add rhubarb; toss to coat.
In another bowl, whisk cream, milk and vanilla; stir into crumb mixture just until moistened.
Turn onto a floured surface; knead gently 4-5 times. Divide dough in half; pat into two 6-in. circles. Cut each into 8 wedges. Place wedges on parchment-lined baking sheets; sprinkle with coarse sugar. Bake 18-22 minutes or until golden brown. Serve warm.
If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.