In a large mixing bowl, combine the dry ingredients. Stir together flour, sugar, baking powder, and salt. Then grate the frozen stick of butter into the mixture and toss together to coat the butter pieces. Add blueberries and stir together.
In a separate bowl, combine sourdough discard, egg, vanilla extract, and 2 Tablespoons of heavy cream. Whisk to combine and then pour into the dry ingredients. Use a fork to mix; the dough will be crumbly.
Dump the dough onto a sheet of parchment paper and use your hands to press the dough together. Shape into an 8" round disc.
Using a bench scraper or large knife, cut the dough across into 8 equal pieces. Place the scones onto a parchment lined baking sheet and place into the fridge to chill for 30 minutes.
While scones are chilling, preheat the oven to 400℉ (204℃). When ready to bake, brush the tops of the scones with more heavy cream (you can also use milk or half and half). Bake for 20-22 minutes until scones are golden brown.
Allow scones to cool and mix together powdered sugar and heavy cream (or milk or half and half) to make the glaze. Add less liquid for a thicker glaze, more liquid for a thinner glaze. Once scones are cooled, drizzle with glaze and serve.