Prep & preheat: Line a baking sheet with parchment. Heat oven to 400°F (204°C).
Dry base: In a large bowl whisk flour, sugar, baking powder, and salt.
Cut in butter: Toss in cold butter. Cut in with a pastry cutter (or grate then toss) until pea-sized bits remain—visible butter = flaky layers.
Add liquids: Stir in vanilla, zest (if using), and most of the cream. Fold with a spatula just until shaggy. If floury patches remain, drip in 1–3 Tbsp more cream; stop the moment it holds together.
Add mix-ins: Sprinkle chosen mix-in over the shaggy dough and fold once or twice to distribute without overworking.
Shape: Tip dough onto a lightly floured surface. Press into a ¾–1-inch thick round (about 7–8 inches wide). Fold the round in half once to stack layers, then press back to a neat round.
Chill: Transfer the round to the prepared sheet. Refrigerate 15–20 minutes (helps height and clean edges).
Cut & finish: Using a sharp knife or bench scraper, cut into 8 wedges in single, confident cuts. Space wedges apart. Brush tops with a little cream; sprinkle coarse sugar for crunch if desired.
Bake: 18–22 minutes, until tops are lightly golden and the centers feel set. Rotate pan once if baking unevenly.
Cool & glaze: Cool on a rack 10–15 minutes. Whisk glaze ingredients until smooth and drizzle over warm scones. Let set 5 minutes.