Place 2 cups unbleached all-purpose flour, 1/3 cup granulated sugar, 1/4 teaspoon baking soda, and 1/4 teaspoon cinnamon into your food processor or a large mixing bowl if you prefer. Pulse a few times or whisk by hand to mix.
Cut 1/2 cup cold unsalted butter into 8 slices and pulse until the mixture looks like oatmeal. Alternately, use a fork or two knives to cut butter into dry ingredients in a bowl.
Pour 1/4 cup 2% or whole milk into a measuring cup and add 1 large egg. Lightly beat with a fork. Add to butter and flour mixture. Pulse until dough just begins to stick together.
Fold in 1 cup fresh blackberries with a spoon using a light touch. If making by hand, lightly stir in egg and milk mixture, then berries, and press dough together to form a loose ball of dough.
Transfer the dough to a floured surface. I like to use a silicone baking sheet so I can throw it into the dishwasher when I'm done. Roll or pat dough into a rectangle shape that is about 1-inch thick. Cut into 12 triangles.
Place onto a cookie sheet covered with parchment paper or a silicone mat. At this point, you can freeze and bake later or go ahead and bake immediately.
Bake for 13-15 minutes. (If baking from a frozen state, you don't have to defrost, but you may need a couple of extra minutes baking time.)
Berry Glaze:
Place 1 tablespoon butter and 2 blackberries into a small, microwave-safe bowl and heat until butter is melted.
Use a fork to smash warm berries into the butter. Add 1 tablespoon heavy cream or half-and-half, 1 cup powdered sugar, and 1 teaspoon vanilla extract and stir until smooth.
Use a spoon to drizzle frosting over slightly cooled scones.