Preheat the oven to 350°F (175°C). Grease a 9-inch (23cm) Bundt pan with soft butter using a pastry brush then lightly spray it with oil to ensure easy release.
In a bowl, combine the sugar and orange zest. Rub the mixture between your fingers to release the oils from the zest, infusing the sugar with a rich orange flavor.
In a separate bowl, mix the milk, white vinegar, and fresh orange juice. Stir to combine.
In a large bowl, whisk together the all-purpose flour, cornstarch, baking powder, baking soda, and salt.
Add the sugar mixture (infused with orange zest) to the dry ingredients and mix well.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Pour the warm, melted butter into the batter and mix until smooth and fully incorporated.
Pour the cake batter into the prepared Bundt pan. Use a spoon to evenly spread the batter, making sure it covers the edges of the pan and fills it evenly.
Place the Bundt pan in the preheated oven and bake for 45-50 minutes, or until the cake is firm to the touch and a toothpick inserted into the center comes out clean.
Once baked, remove the Bundt pan from the oven and let the cake cool in the pan for about 25 minutes. Afterward, gently flip the cake onto a serving plate and tap the pan to release the cake.
In a small bowl, mix the orange juice, powdered sugar, and melted butter. Stir until smooth.
Pour the orange glaze evenly over the cooled cake. Let the glaze set for a few minutes before serving.
Slice and serve!