Toss fresh rhubarb pieces and 3 tablespoons of sugar in a small bowl until rhubarb is completely coated and set aside
Sift together flour, sugar, baking powder and salt in a large mixing bowl
Add the cold cubes of butter and work the butter into the flour mixture until the constancy resembles corn meal - feel free to use your hands or a pastry cutter
In a measuring cup, whisk together the buttermilk, egg and vanilla
Pour the buttermilk mixture into the large bowl with the flour mixture and mix with a rubber spatula until just combined
Add in sugared rhubarb and mix until incorporated
Scrape the dough onto a floured work surface or pieces of parchment paper, give it a quick kneed and form a a circle that is about 6 inches in diameter
Cut into 8 wedges and move wedges to a parchment paper lined baking sheet placing them about 2 inches apart
Refrigerate for 20 minutes, uncovered
Preheat oven to 400°F
Brush scones with melted butter and bake until golden brown. About 20 minutes