250g butter, softened, plus more for pan (I used salted butter)
225g all-purpose flour, sifted, plus more for pan
Finely grated zest of 1 orange (about 2 teaspoons zest)
1/2 teaspoon pure vanilla extract
5 large eggs, room temperature
Preheat oven to 160C with rack in lower third. Grease and flour two 6″ bundt pan. Whisk in the orange zest with the flour and salt in a small bowl. Set aside.
Put butter into the bowl of an electric mixer fitted with the paddle attachment. Cream on medium speed until pale and fluffy, scraping down sides of bowl as needed, about 4 minutes. Add sugar. Mix until pale and fluffy, scraping down sides of bowl as needed, about 3 minutes.
Mix in vanilla. Add eggs, 1 at a time, mixing well after each addition; mix until smooth. Reduce speed to low. Add flour mixture in 3 batches, mixing until just combined after each addition.
Spoon batter into pans and smooth tops using a small rubber spatula. Firmly tap the pan on counter to eliminate any air bubbles. Bake until a cake tester inserted into centers comes out clean, about 40-45 minutes. Let cakes cool slightly in pan on a wire rack, about 10 minutes. Run a knife around edges of molds to loosen; unmold cakes.