Mix wet ingredients: In a medium mixing bowl or measuring glass, whisk together 170 g sourdough discard, 1 large egg, 65 g heavy cream or half-and-half, and ½ teaspoon vanilla extract. If your kitchen is warm, cover refrigerate until needed.
Mix dry ingredients: In a large mixing bowl, whisk together 235 g all-purpose flour, 4 teaspoons baking powder, and ½ teaspoon fine sea salt until combined. Toss in 140 g unsalted butter (cold and cut into ½" cubes, or frozen and grated) until all of the pieces are coated in flour. Use your fingertips or a pastry blender to work the pieces into the flour mixture until it resembles coarse bread crumbs with a few larger pieces that are no bigger than peas.
Add the mix-ins: Toss in 55 g dried cranberries and 85 g white chocolate chips or chunks and mix in until evenly distributed.
Add the wet ingredients: Add the discard and cream mixture and toss in with a rubber spatula or your fingers until the flour is evenly hydrated and the dough just holds together when squeezed. Pour it out onto a clean work surface and pat into a circle that's about 8" (20.3 cm) in diameter and 1" (2.5 cm) thick. Wrap in plastic wrap and refrigerate at least 2 hours and up to 2 days.
Bake: Preheat the oven to 400˚F (200˚C) and line a baking sheet with parchment paper or a silicone baking mat. Cut the disc of dough into 8 wedges, and arrange the wedges on the baking mat. Cover the baking sheet and freeze or refrigerate the raw scones while the oven preheats (and for at least 30 minutes). Brush the tops of the scones with 2 tablespoons heavy cream and sprinkle on 2 tablespoons coarse sugar. Bake until puffed and just starting to turn golden on the edges, or about 16-20 minutes.
Cool & Finish: Let the scones cool on the baking sheet for 5-10 minutes, then transfer to a wire rack to cool completely. Whisk together 115 g powdered sugar and 2 tablespoons heavy cream or half-and-half and drizzle over the cooled scones. You can add a little more powdered sugar to make the glaze thicker, or a little more cream to thin the glaze out as desired.
Enjoy! Scones are best eaten the day they're made, but will keep at room temperature in an airtight container for up to 3 days.
