Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.

Whisk the flour, sugar, baking powder, salt, cinnamon, and orange zest together in a large mixing bowl. Add the butter and work it into the flour mixture using a pastry cutter or your fingertips until the mixture resembles coarse crumbs.

Add the rhubarb and toss gently to distribute evenly.

In a small bowl, whisk the heavy cream, egg, and vanilla extract together. Pour the mixture into the dry ingredients and stir just until a shaggy dough forms. Do not overmix. If the dough feels overly sticky, add 1-2 tablespoons additional flour.

Turn the dough onto a lightly floured surface and gently press it together into a circle approximately 1 inch thick. Cut into 8 wedges and transfer to the prepared baking sheet, spacing the scones slightly apart.

Brush the tops with the remaining tablespoon of heavy cream and sprinkle with turbinado sugar, if using. Bake for 18-22 minutes, or until lightly golden around the edges and set in the center.