1. Preheat oven to 325 degrees with rack in lower third. Butter a 9-by-5-inch loaf pan. In a bowl, whisk together flours, baking powder, and salt. With a vegetable peeler, peel zest from half of orange into about 5 strips; squeeze and reserve 2 teaspoons juice. Pulse zest strips with granulated sugar in a food processor until finely ground.

2. In another bowl, beat butter and cream cheese on medium until smooth. Add orange-sugar mixture; beat on high until pale and fluffy, about 5 minutes. Beat in vanilla and eggs, one at a time, on medium. Add flour mixture; beat on low until just incorporated. Pour batter into pan; smooth top with a spatula.

3. Bake, rotating pan halfway through, until cake is golden brown and a tester inserted in center comes out clean, 1 hour, 15 minutes. (If browning too quickly, tent with foil.) Let cool 30 minutes in pan on a wire rack. Remove from pan; let cool completely on rack, about 2 hours.

4. In a bowl, whisk together confectioners' sugar, reserved orange juice, and liqueur until smooth. Spread glaze over cake; sprinkle finely grated zest from remaining orange half over top.