Preheat the oven to 350°F (175°C). Grease and flour a cake pan.

In a mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

Add the egg, milk, vegetable oil, and vanilla extract to the dry ingredients and mix until smooth.

Pour the batter into the prepared cake pan and bake for 30 minutes or until a toothpick comes out clean.

Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

In a small saucepan, combine the powdered sugar, orange juice, and orange zest. Stir until smooth.

Once the cake is completely cooled, drizzle the orange glaze over the top.