Prep the oven and pan. Heat oven to 400°F (200°C).
Line a baking sheet with parchment paper.
Mix dry ingredients. In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt until well combined.
Cut in the butter. Add the cold butter cubes. Use a pastry cutter or your fingertips to work the butter into the flour until pea-sized bits remain. Keep some larger, flat pieces for flakiness.
Combine wet ingredients. In a small bowl, whisk cream, buttermilk, egg, and vanilla until smooth.
Keep this mixture cold.
Add raspberries. Gently toss raspberries into the flour-butter mixture. Don’t overmix—some berries will break, which is fine.
Bring the dough together. Pour the wet mixture over the dry. Stir with a fork just until a shaggy dough forms.
If it looks dry, add 1–2 teaspoons more cream. The dough should be slightly sticky, not wet.
Shape. Turn the dough onto a lightly floured surface. Pat into a 7–8 inch (18–20 cm) round, about 1 inch (2.5 cm) thick.
Use a bench scraper to tidy the edges if it crumbles.
Cut. Slice the round into 8 wedges. Transfer to the prepared sheet, spacing them apart. Brush tops with a little cream and sprinkle with coarse sugar if using.
Chill briefly. For the best rise, place the tray in the fridge or freezer for 10 minutes to re-chill the butter.
Bake. Bake for 16–20 minutes, until golden on the edges and set in the center.
If using frozen berries, add a minute or two.
Cool and glaze. Let scones cool on the pan for 10 minutes, then move to a rack. Whisk glaze ingredients until smooth and thick but pourable. Drizzle over warm scones.
Let set for 5–10 minutes.