Preheat oven to 400º. Place parchment paper on cookie sheet or pizza pan and set aside.
In a large bowl, combine flour, brown sugar, baking powder and salt.
Cut in butter until mixture is crumb sized.
In a medium bowl, combine the wet ingredients. Pour wet ingredients into dry ingredients and stir until just combined.
Fold in rhubarb.
Flour a counter or cutting board, and place dough onto the floured surface.
Press out the dough until it's a 1/2" thick circle. Place onto prepared cookie sheet and cut into 8 even wedges.
Bake for 16 minutes, or until golden.
While scones are cooling, whisk together powdered sugar and vanilla in a small bowl.
Add whipping cream 1 Tbsp. at a time, until desired consistency is reached.
Drizzle glaze over the scones. Best eaten warm.