Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper or a silicone mat. Freeze or grate the butter, and dice the peach.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, salt, and cinnamon until evenly combined.
Add the grated or cubed cold butter to the dry ingredients. Toss with your fingertips or a pastry cutter until the mixture looks like coarse crumbs with some pea-sized bits of butter still visible.
Gently fold the diced peach into the flour and butter mixture, coating each piece so they stay separated instead of clumping.
In a separate small bowl, whisk together the cold heavy cream, egg, and vanilla extract until smooth.
Pour the wet mixture into the dry mixture and stir gently with a fork or rubber spatula just until a shaggy dough forms and no dry flour remains.
Turn the dough out onto a lightly floured surface and pat it into an 8-inch (20cm) circle, about 1 inch (2.5cm) thick. Use a bench scraper to cut into 8 even wedges.
Transfer the wedges to the prepared baking sheet, spacing them about 2 inches (5cm) apart. Brush the tops with cream, sprinkle generously with turbinado sugar, and bake for 16 to 18 minutes until golden brown.
Let the scones cool on the baking sheet for 5 minutes, then transfer to a wire rack. If using the glaze, whisk together powdered sugar, milk, and vanilla, then drizzle over the cooled scones.