Preheat oven to 350°F. Grease a 10–12 cup Bundt pan with butter, then dust with flour.
Whisk flour, baking powder, baking soda, and salt in a bowl. Set aside.
Beat softened butter, granulated sugar, and brown sugar until pale and fluffy, about 3 minutes.
Add eggs one at a time, mixing well. Blend in vanilla and orange zest.
Mix in sour cream until smooth.
Stir orange juice and buttermilk together in a small cup.
Add dry ingredients to the batter in three additions, alternating with the buttermilk mixture. Mix just to combine.
Toss cranberries with 1 tbsp flour, then gently fold them into the batter.
Spoon batter into the pan and smooth the top. Tap the pan to release air bubbles.
Bake 48–55 minutes, until a tester comes out clean and the top springs back.
Cool in pan 15 minutes. Invert onto a rack and cool completely.
Whisk confectioners' sugar, orange juice, zest, vanilla, and a pinch of salt until thick and pourable. Drizzle over cooled cake.