Step 1

Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 10-inch fluted tube pan (such as Bundt®).

Step 2

Sift flour, baking powder, salt, and baking soda together in a bowl; set aside.

Step 3

Beat white sugar and butter together in a large bowl with an electric mixer until light and fluffy, about 3 minutes. Beat in eggs one at a time, then beat in vanilla extract and orange zest. Add flour alternately with sour cream in 3 additions, beginning and ending with flour. Beat until smooth. Scrape the sides of the bowl with a rubber spatula. Spread evenly in the prepared pan.

Step 4

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour and 15 minutes. Cool on a wire rack for 10 minutes, then unmold the cake onto the wire rack to cool completely.

Step 5

While the cake is cooling, bring orange juice, sugar, and orange zest to a boil in a small saucepan over medium-high heat. Reduce heat and cook until syrupy, about 15 minutes. Remove from heat and whisk in butter, 1 tablespoon at a time. Drizzle warm syrup over cake slices.