Preheat oven to 375℉ (191℃).
In a large bowl, whisk the flour, granulated sugar, baking powder, baking soda, and salt together to combine.
3 cups (423g) all-purpose flour, 1/3 cup (67g) granulated sugar, 2 teaspoons baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon salt
Add the cold butter by grating it on the large holes of a box grater and tossing with the flour mixture to coat or by cutting it in with a pastry cutter until only pea-sized pieces of cold butter remain. It is important that the butter stay cold at all times.
1/2 cup (113g) salted butter
In another bowl, whisk the egg and cream together. Pour the wet ingredients into the flour mixture and stir with a fork just until a shaggy dough starts to come together. It is okay if there are still some dry spots.
1 large egg, 1 1/4 cups (300g) heavy cream
Sprinkle the blackberries over the dough and lightly knead the dough to incorporate the berries, being careful not to crush them too much. *If using frozen berries, toss them with a couple teaspoons of flour first so they don't streak the dough.
1 cup blackberries
Turn out the scone dough onto a sheet of parchment paper or plastic wrap and pat into a circle about 1" thick. Cut into 8 wedges with a sharp knife or bench scraper, then transfer to a parchment-lined baking sheet.
Brush each scone with a little cream using a pastry brush and sprinkle with coarse sugar. Bake for 25-30 minutes, until the scones are golden brown. Remove from oven. Serve warm or continue with the next step to add a honey butter glaze.
Coarse sugar
While the scones are baking, make the glaze (if desired) by microwaving the honey and butter in a microwave safe bowl for 1-1/2 minutes. When the scones are done baking, remove them from the oven and brush with half of the honey butter glaze, then cool for 15 minutes, and brush again with the remaining glaze. Serve warm.
1/3 cup honey, 1/4 cup salted butter