Heat the oven and prep the pan: preheat the oven to 350°F. Grease a 12-cup bundt pan thoroughly with baking spray or butter, getting into every flute, then dust lightly with flour and tap out the excess.
Whisk the dry ingredients: in a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
Cream the butter, sugar, and zest: in a large bowl, beat the softened butter with the sugar and orange zest on medium speed for 3 to 4 minutes, until pale and fluffy. The zest rubbed into the sugar releases the orange oils and perfumes the whole cake.
Add the eggs and vanilla: beat in the eggs one at a time, then the vanilla, scraping down the bowl as needed.
Alternate wet and dry: mix in the sour cream and orange juice, then add the dry ingredients in two additions, mixing on low just until no flour streaks remain. Do not overmix.
Fold in the cranberries: toss the cranberries with 1 tablespoon of flour, then fold them gently into the batter with a spatula.
Fill and bake: spread the batter evenly in the prepared bundt pan and smooth the top. Bake at 350°F for 55 to 60 minutes, until a long toothpick inserted in the center comes out clean (check a few spots — you may hit a berry).
Cool and release: cool the cake in the pan for 20 minutes, then invert onto a wire rack and cool completely, about 1 hour. A fully cooled cake glazes cleanly; a warm cake melts the glaze off.
Glaze and garnish: whisk the powdered sugar, 3 tablespoons of orange juice, and the zest until smooth and pourable, adding the last tablespoon of juice only if needed. Drizzle over the cooled cake so it drips down the flutes, then crown with sugared cranberries if using.