A plain-Jane cake gets dolled up with aromatic orange juice and zest in the batter.
Preheat oven to 325 degrees. In a large bowl, whisk together flour, baking powder, salt, and 1 cup sugar. Make a well in center of flour mixture. Add oil, egg yolks, orange zest and juice, and 1/4 cup cold water; whisk batter until smooth.
Using an electric mixer, beat egg whites and cream of tartar until soft peaks form. Gradually add remaining 1/2 cup sugar (1 tablespoon at a time); continue to beat until stiff peaks form. Using a rubber spatula, gently fold half of egg-white mixture into batter. Fold in remaining egg-white mixture just until combined (do not overmix).
Pour batter into a 10-inch footed angel-food cake pan with a removable bottom; bake until a toothpick inserted near center of cake comes out clean, 55 to 60 minutes. Remove from oven; invert, still in pan, onto a baking sheet. Cool completely. Run a knife around edge and center to release cake. Serve topped with vanilla whipped cream and candied orange zest, if desired.