Preheat the oven to 400°F and line a baking sheet with parchment. You can also use a round pizza stone with or without parchment.
Wash the rhubarb and cut off the leafy stalk and the end. Cut the rhubarb into 1/2" pieces.
In a large bowl or food processor, combine flour, brown sugar, baking powder, and salt.
Add butter into the dry ingredients. Use your hands to massage the mixture until it is a fine sand. You could use a pastry cutter or forks to cut the butter until mixture is well blended. Or combine the butter with the dry ingredients and pulse it a bunch of times in the food processor, until the mixture is crumbly.
In a large bowl, combine whipping cream, egg, and vanilla. Pour the dry ingredients into the wet ingredients and stir until just combined. Gently fold in rhubarb.
Add a sprinkling of flour to a counter or a cutting board. Place the dough on the floured surface.
Press the dough out into a circle (or separate into two circles) that is about 1/2 inch thick. Place onto prepared baking sheet, separating the wedges by 1/4-1/2 inch.
Scones need to be baked for 22-25 minutes. They should be a light golden brown.