Preheat oven to 400 degrees Fahrenheit. Line a rimmed baking sheet with parchment paper and set to the side.
Zest blood oranges into a large mixing bowl. Add granulated sugar and, using your fingers, vigorously rub the zest into the sugar. The sugar should become fragrant and turn a light shade of orangish pink.
To the same bowl, add in the all-purpose flour, baking powder, and salt. Use a whisk to combine everything together.
Add butter to the bowl and using your fingers or a pastry blender, mix the butter into the flour mixture until it is the size of peas. Stir in the currants. Add buttermilk and using a fork or heavy duty spatula, stir the mixture until it forms into a shaggy dough.
Turn the dough out onto a lightly floured work surface. Gently pat the dough into a rectangle, about 1-inch thick. Fold the dough in half then pat it down into a rectangle angle. Repeat the process about 2 more times. Pat the dough into an 8-inch by 8-inch square that is approximately 1 inch thick. Use a sharp knife or bench scraper to cut evenly into 6 triangles or squares.
Transfer the scones to the prepared baking sheet. Brush the top of each scone with the half and half or cream. Sprinkle with turbinado sugar, if desired.
Bake scones for 20 to 25 minutes, until they are golden brown and cooked through.
Scones are best enjoyed on the day made. However, you can store any leftover scones in an airtight container or resealable bag for up to 2 days. They can also be frozen for up to 2 months.