Add the cold cubed unsalted butter to the dry ingredients. Using a pastry cutter, two forks, or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with pea-sized bits of butter remaining (about 6–8 rotations with a pastry cutter). Work quickly to keep the butter cold.

Combine Wet Ingredients

In a small bowl or measuring cup, whisk together the heavy cream, whole milk, egg, and vanilla extract until smooth.

Form Dough

Make a well in the center of the dry mixture and pour in about three-quarters of the cream mixture. Using a rubber spatula or wooden spoon, gently fold the wet into the dry until the dough just comes together. If the dough seems dry, add the remaining cream mixture a tablespoon at a time until it holds together but is not sticky. If using optional mix-ins, fold them in gently at this stage (do not overmix).

Shape and Cut

Turn the dough out onto a lightly floured surface and gently pat it into a disk about 1-inch (2.5 cm) thick. Using a sharp knife or bench scraper, cut the disk into 8 wedges (like a pie). Alternatively, you can pat into a 2-inch thick disk and cut with a 2.5-inch round cutter for round scones. Handle the dough as little as possible to retain flakiness.

Bake Preparation

Place the wedges or rounds on the prepared baking sheet spaced about 1 inch apart. Brush the tops lightly with additional heavy cream to help browning, and sprinkle with coarse sugar if desired.

Bake

Bake in the preheated 400°F (205°C) oven for 15–20 minutes, rotating the pan once halfway through baking, until the scones are golden brown on top and a toothpick inserted into the center comes out clean. Baking time will vary slightly with oven and size of scones.

Cool and Serve

Remove the scones from the oven and transfer to a wire rack to cool for 5–10 minutes. Serve warm or at room temperature with clotted cream, butter, jam, or honey as desired.