1. Preheat oven to 400 degrees. Whisk together 3/4 cup cream and egg. In a large bowl, whisk together flour, granulated sugar, baking powder, and salt.
2. With a pastry blender or 2 knives, cut butter into flour mixture until it resembles coarse meal, with a few pea-size pieces of butter remaining. Stir in cranberries, zest and walnuts. With a fork, stir in cream mixture until just combined. (The dough should be crumbly; do not overwork.)
3. Transfer dough to a lightly floured work surface and pat into a 6-inch circle. Cut into 6 wedges and transfer to a parchment-lined baking sheet. Brush tops with 1 tablespoon cream and sprinkle with sanding sugar, if desired. Bake until golden, 16 to 18 minutes, rotating sheet halfway through.