• Preheat the oven to 175°C (350°F) with top and bottom heating mode. Prepare the bundt pan, pastry brush and shortening, vegetable oil spray, or softened butter for greasing. Do not grease the pan until just before filling with batter.

For the meringue

• In a stand mixer fitted with a whisk or with handheld beaters, whip egg whites with cream of tartar at medium-high speed until foamy. Gradually add the sugar and continue whipping until stiff peaks form. Set aside.

For the batter

• Sift together the plain flour, baking soda and salt into a mixing bowl.
• Switch to a paddle attachment on the stand mixer (or use handheld beaters). Beat butter with the remaining sugar at medium speed until light and fluffy, about 4 - 6 minutes, stopping once or twice to scrape down the sides of the bowl.
• Beat in egg yolks, one at a time, making sure each is well incorporated into the butter mixture before adding the next. Add the orange juice and grated zest and beat until well mixed, about 10 - 15 seconds.
• Reduce the mixer speed to low. Add the flour mixture in three additions alternating with the yogurt, beginning and ending with the flour mixture. Mix in each addition until just combined, making sure not to over mix the batter, just enough to get the batter smooth and creamy.
• With a rubber spatula, fold the meringue into the mixture. Do this in 3 additions until thoroughly incorporated and the batter is smooth and of the same consistency throughout.
• Grease the bundt pan thoroughly with shortening, vegetable oil spray or softened butter. Make sure the grease gets into all the grooves. Sprinkle flour liberally over the grease and tap out the excess.
• Spoon the batter into the prepared pan. Level the batter and smooth the surface with a rubber spatula. Bake in the centre of the oven for 45 - 50 minutes, or until the cake tests done. If the cake browns too quickly before it is done, cover the pan with a sheet of aluminium foil. To check, insert a metal skewer or cake tester into the centre of the cake. If it comes out clean, it is done. If it comes out sticky or covered in batter, add 5 - 7 minutes to the baking time.
• Remove the pan from the oven and let the cake cool in the pan for 10 - 15 minutes. Invert the cake onto a wire rack to finish cooling.

Make the simple orange syrup (optional)

• In a small saucepan, combine orange juice and sugar. Heat over medium heat, stirring frequently until the sugar dissolves. Remove from heat and let the syrup cool a while. While the cake is still warm, brush with syrup all over using a pastry brush. Let the cake sit for 30 minutes to fully absorb the syrup.

Make the orange cream cheese glaze

• In a mixing bowl, combine all the ingredients. Mix or stir with a rubber spatula or wooden spoon until smooth - the mixture will be thick and pasty. Warm in a microwave oven on low power setting for 15 seconds, or until it is at a pourable (but not runny) consistency. Allow the glaze to firm up slightly before drizzling over the cake.

Decorate the cake

• Spoon the glaze on the top of the cake, using the spoon to gently nudge it down the sides of the cake where desired. Let the glaze set. Just before serving, grate fresh orange zest over the glaze and place fresh-cut orange slices on top if desired.