Using the large holes of a box grater, grate 8 Tablespoons cold unsalted butter onto a large plate. Put the plate in the freezer to chill while you prep the rest of the ingredients.
Wash and dry the outside of your naval orange well. Use a microplane or zester to completely zest the orange. Measure out 1 teaspoon of the zest and put it in a measuring cup. Squeeze the juice from the orange into the measuring cup. Add enough plain Greek yogurt to the orange juice mixture to measure a total of 1/2 cup (my juice was just under 1/4 cup, so I needed just over 1/4 cup of yogurt to get up to the 1/2 cup mark, but it will depend on your orange). Stir 1 large egg into the orange juice mixture and set the mixture aside.
In a large bowl, whisk together 1 ½ cups all-purpose flour, ½ cup whole wheat flour, ⅓ cup granulated sugar, 1 teaspoon baking powder, ½ teaspoon salt, and ¼ teaspoon baking soda.
Mix the chilled grated butter into the flour mixture until the butter is evenly distributed. Using a spatula, stir the orange juice mixture into the flour mixture until all of the liquid has been absorbed. Dump the flour mixture onto a clean working surface and knead the dough until all of the flour has been absorbed (try to limit contact with your hands as much as possible to avoid melting the butter). Pat the dough into a 4x6" square, wrap in plastic, and place in the freezer for 10-15 minutes to chill.
Move the oven rack to the middle position and turn the oven on to 400°F. Prepare a baking pan by lining it with parchment paper or a silicone baking mat.
If the dough is sticky, dust the top and bottom very lightly with flour. Roll the dough into a 12x12" square. Sprinkle 1 cup frozen or fresh cranberries and ½ cup white chocolate chips or chunks evenly over the dough and gently press both into the dough.
From the bottom, carefully roll the dough upwards, as if making cinnamon rolls (using a bench scraper to help "peel" the dough from the counter really helps here). Don't worry if the dough doesn't roll smoothly, this is just a way of distributing the mix-ins.
Once the dough is all rolled, press the dough into a 4x12" rectangle. Cut the rectangle in half (you will now have two 4x16" rectangles), then each half in half. Cut each of those four 3x4" rectangles in half diagonally so that you have 8 triangles.
Place the triangles on the prepared baking sheets, ideally with the cut edges to the sizes, but place them however they seem the most stable. If desired, sprinkle a little bit of coarse sugar (sanding sugar or demerara sugar) on the tops of the scones. Bake for 17-20 minutes, until the tops are browned and the centers seem set (I checked mine at 15 minutes, and while at first they looked done, a gentle touch revealed that the centers were still very doughy). Cook on the baking sheet, and drizzle with melted white chocolate, if desired.
Notes
Make-Ahead Instructions:If you want to enjoy these scones fresh-baked in the morning without having to wake up a couple of hours early to make them, you can make them the day before and refrigerate before baking.Follow the recipe to the end of step 8. Place the cut scone dough in an airtight container (make sure it's large enough that they're not squished together) or set them on the baking sheet and cover it completely with plastic wrap. Bake as directed the morning you plan to serve them (you might need to add up to 5 minutes to the baking time as they will be extra cold). Note that if you're using frozen cranberries, the cranberries will thaw in the dough before baking, and may weep a bit of their juice before baking. This should be fine, as this will occur with baking anyway.Alternatively, you can bake them the night before you plan to serve them, and cover with a clean towel overnight. Reheat in a low oven (250-300°F) for about 10 minutes, or in the microwave.