Preheat the oven to 350°F (175°C).
Prepare an 8″ springform pan by spraying with oil (or butter) and lining with parchment paper (sides optional for cleaner sides), then spray the paper as well.
Place the sugar and eggs in a large bowl and beat with a mixer until light and fluffy.
Sift the flour with the baking powder or Paneangeli, then add to the mixture in the bowl a little at a time along with the softened butter. Continue to mix until completely blended, then stir in the yogurt.
In a food processor, process the whole orange until it is almost pureed.
Add this orange puree to the cake mixture (along with the vanilla if you used plain baking powder) and stir until evenly combined. Pour the batter into the prepared tin.
Bake for 50-60 minutes (depending on your oven), but test with a cake tester or skewer to ensure the orange cake is done before removing it from the oven. Allow to cool for about 15 minutes, then remove the side of the springform pan.
For the Orange Glaze:
Prepare the glaze by melting the sugar in the orange juice and allow to simmer for a few minutes until the liquid has a syrupy consistency.
Spoon and brush the glaze over the top of the cake and allow it to cool completely before cutting.