Preheat your oven to 175 degrees Celsius (350 degrees Fahrenheit) and let it heat for 15 minutes.

Grease a 9-inch round cake pan with butter and dust with flour. Alternatively, line the base with parchment paper.

Let your eggs and butter sit at room temperature for at least 30 minutes.

Zest the oranges before juicing them.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, combine the granulated sugar and fresh orange zest. Rub them together until fragrant.

Add the softened butter and beat until pale and fluffy. Then add the vegetable oil and beat for another 30 seconds.

Add eggs one at a time, beating well after each addition. Mix in the vanilla extract.

In a separate bowl, combine the fresh orange juice and sour cream. Gradually mix this into the butter mixture, alternating with the dry ingredients, until just combined.

Pour the batter into the prepared pan and smooth the top. Bake for 38 to 42 minutes until golden and a toothpick comes out clean.

Let the cake cool for 15 minutes in the pan before transferring it to a wire rack.

While the cake bakes, heat the orange juice and sugar for the syrup in a small saucepan until the sugar dissolves. Simmer for 2 minutes.

Poke small holes in the cake and brush the syrup over it after baking.

Whisk together powdered sugar, orange juice, and zest until you reach a thick but pourable consistency.

Pour the glaze over the cooled cake and let it set for 15 minutes before serving.