How to Make It
Preheat the oven to 350°. Butter and flour two 8 1/2-by-4 1/2-inch loaf pans. In a medium bowl, whisk the flour with the baking powder and salt.
In a large bowl, using a handheld electric mixer, cream 2 sticks of the butter with the cream cheese at moderate speed. Add the sugar and orange zest and beat until light and fluffy, about 2 minutes. Add the eggs, 1 at a time, beating well between additions. Beat in the vanilla. Add the dry ingredients and beat at low speed until blended. Add the sour cream and beat until smooth. Divide the batter between the prepared pans and smooth the surfaces.
Bake the pound cakes for about 1 hour, or until the tops are golden and cracked and a toothpick inserted in the centers comes out clean. Let cool in the pans for 15 minutes, then turn the pound cakes out onto a rack and set them right side up to cool completely.
Cut the passion fruits in half and scrape the seedy fruit into a strainer set over a bowl. Press the fruit with the back of a spoon; discard the seeds. Melt the remaining 1/2 stick of butter in a small saucepan. Add the confectioners' sugar and passion fruit juice; cook over very low heat, stirring, until smooth. Drizzle the icing over the cakes, letting it drip down the sides. Let the icing set, then slice the cakes and serve.