TO MAKE THE CAKE BATTER:
- Adjust oven rack to lower middle position and preheat the oven to 350F/180C (325F/160C if using a dark pan).
- Generously grease and flour (or spray with a non-stick cooking spray) a 6-cup bundt pan* (*see note). Set aside.
- In a medium bowl, whisk together the flour, cornstarch, baking powder, baking soda and salt. Set aside.
- In the bowl of a stand mixer fitted with a paddle attachment (or in a large bowl and an electric hand mixer), beat the butter on medium speed until creamy, about 1 minute.
- With the mixer running on medium-low speed, gradually add in the sugar, followed by both orange and lemon zest. Raise the speed to medium-high and continue beating together until lightened up in both color and texture; 4 to 5 minutes. The color should turn very pale (almost white) and texture should look fluffy.
- Add the eggs, one at a time, beating well after each addition. Add in the vanilla and sour cream, mixing until well incorporated.
- On lowest speed, add in one-third of the flour mixture and mix until mostly combined. Add in half of the orange juice and lightly stir until almost mixed in. Continue with adding another one-third of the flour mixture, followed by the remaining orange juice and ending with the last third of flour mixture. Mix until just combined and a smooth batter forms. Do not overmix. With a rubber spatula, give the batter one good, final stir to make sure that everything is well incorporated. Transfer the batter to the prepared pan and smooth the top.
- Bake for 25 to 30 minutes, or until the center of the cake springs back when lightly touched, and a wooden skewer inserted between the tube and sides comes out clean or with a few cooked crumbs attached.
- Transfer the pan to a wire rack and cool slightly. Meanwhile, make the orange syrup, if using.
TO MAKE THE ORANGE SYRUP:
- In a tiny saucepan over very low heat, bring together the orange juice and sugar to a simmer until the sugar is dissolved. Remove from the heat once it reaches a simmer. Using a thin skewer, poke tiny holes all over the cake. Brush the surface of the cake with about one-third of the syrup. Let the cake cool in the pan for 10 minutes, then invert onto a serving platter. Brush the top and sides of the cake with the remaining syrup. Allow the cake to cool slightly before serving, or wait until its barely warm before glazing (if using); at least 40 more minutes.
TO MAKE THE CREAM CHEESE GLAZE:
- In a medium bowl, whisk the cream cheese until smooth. Add in the powdered sugar, and whisk together until no longer lumpy. Whisk in enough heavy whipping cream to get the mixture to a thick, yet pourable consistency.
- Pour the glaze all over the cake then give it enough time to set. Garnish with strands of orange peel, if desired.
- Cut into slices and serve. Store leftovers in an airtight cake dome at room temperature for 3 to 4 days.