Preheat oven to 400ºF (200ºC).
Line a baking or cookie sheet with parchment paper or grease the bottom.
In the food processor: place 2 ¾ cups all-purpose flour, 1 tablespoon baking powder, ¼ teaspoon salt, 7 tablespoons sugar and ½ teaspoon lemon zest in the bowl of a food processor fitted with the steel blade. Pulse a few times to mix.
Scatter the cold butter cubes on top, and process on low until the mixture is grainy and the butter the size of peas. Don't overprocess.
By hand: stir to mix 2 ¾ cups all-purpose flour, 1 tablespoon baking powder, ¼ teaspoon salt, 7 tablespoons sugar in a large bowl. Add ½ teaspoon lemon zest and stir to mix with a spoon or rubber spatula.
Scatter 6 ounces unsalted butter pieces on top and integrate by hand or with a pastry cutter. The pieces of butter should be the size of peas and beans. It will be irregular. For both methods: transfer the mixture to a large mixing bowl and add 1 ½ cups raspberries. If using frozen raspberries, don't thaw them. Mix lightly with a spoon or rubber spatula.
Drizzle ½ cup buttermilk and ¼ cup heavy cream over the flour mixture.
Mix with a fork until it barely comes together, but don't mix too much, or the scones will be tough and flat.
On a lightly floured surface, transfer the mixture and pat it together, folding it unto itself a few times until you have a circle of dough that holds together (I use a dough scraper). It will still be shaggy in places. Don't be tempted to overwork it as you would a pie crust. I don't use a rolling pin, but if you want to, roll it very lightly, you don't want to press it down, simply pat it so it holds together. Make a circle with the dough, about 2 inches high.
Cut it in half, and then cut each half into 4 triangles. You should have 8 pieces or triangles.
At this point, they can be frozen, well covered, for up to a month, and baked directly from the freezer. They might take a few more minutes.
Transfer to the prepared baking sheet, and sprinkle the tops with extra sugar.
Bake for 15 minutes, turn down the oven temperature to 350°F (180°C) and bake for an additional 20-25 minutes, or until golden brown and dry. If you need to check, with the tip of a fork lift the top of a scone and see if the inside is dry. Depending on the size and height, the bake time might vary, so start checking at the 30-minute mark.
I recommend eating them within a few hours of being baked.
Store leftovers in an airtight container for a day, maybe two, but the texture is much better the day they're baked.