Preheat the oven: Set your oven to 425°F and line a baking sheet with parchment paper.
Mix dry ingredients: In a large bowl, combine the whole wheat flour, sugar, baking powder, baking soda, lemon rind, and salt.
Cut in the butter: Add the cold, cubed butter to the flour mixture. Use a pastry cutter or your hands to work the butter into the flour until the mixture resembles coarse crumbs (you should still have pea-sized pieces of butter).
Add wet ingredients: In a separate bowl, whisk together the sourdough starter discard, milk, egg, lemon juice, and vanilla (if using). Stir until the mixture is smooth.
Combine the dough: Pour the wet ingredients into the dry mixture and stir until just combined. The dough will be a little sticky. Be careful not to overwork the dough.
Add blueberries: Gently fold the blueberries into the dough. If you’re using frozen blueberries, don’t thaw them beforehand to prevent them from bleeding too much into the dough.
Shape the scones: Turn the dough out onto a lightly floured surface and gently pat it into a round disc about 1 inch thick. Cut the dough into 8 wedges (like a pizza) or shape it into smaller rounds, if you prefer. Place the scones on the parchment-lined baking sheet.
Bake: Bake for 10-13 minutes, or until the scones are golden brown on top and firm to the touch.
Glaze (optional): While the scones are cooling, whisk together the powdered sugar, and lemon juice. Drizzle it on top of the scones once they have cooled slightly.
Serve: Serve warm or at room temperature. These scones are perfect for breakfast or an afternoon snack!