• Line two rimmed baking sheets with parchment paper, or spray with non-stick cooking spray.
• In a large mixing bowl add the flour, sugar, baking powder, baking soda, and salt. Whisk to blend.
  270 grams all-purpose flour, 100 grams sugar, 1 tablespoon baking powder, ½ teaspoon baking soda, 1 teaspoon salt
• Set a box grater in the bowl of flour mixture and using the largest shred side, grate the cold stick of butter into the flour mixture. Remove the box grater and toss the shredded butter with the flour to coat and break up even smaller.
  113 grams butter
• Make a well in the center of the bowl with the flour mixture. Add the sour cream, vanilla extract, and the frozen diced rhubarb to the well. Using a spatula, quickly mix the ingredients, scraping the sides to incorporate all the flour.
• Turn the dough out onto a lightly floured work surface. Flour your hands and pull the dough together to form an 8 inch diameter disc.
• Using a sharp knife or bench scraper, cut the disc into 8 equal wedges. Transfer the wedges to the prepared baking sheets and let them sit to rest for 10 minutes (this activates the baking powder and gives a better rise when baking).
• Preheat the oven to 375℉ while waiting for the scones to rest.
• Bake in the preheated oven for 20 - 22 minutes, or until just starting to turn golden brown. Remove and cool completely before drizzling with the lemon icing glaze.

Lemon Icing Glaze

• In a small bowl, mix the powdered sugar and lemon juice. Stir with a whisk until creamy with no lumps.