Follow these straightforward steps to create Moist Orange Sheet Cake:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 13×9-inch baking pan.
2. Mix Dry Ingredients: In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.
3. Combine Wet Ingredients: In another bowl, mix the whole milk, fresh orange juice, vegetable oil, eggs, orange zest, and vanilla extract. Whisk until smooth.
4. Combine the Mixtures: Gradually pour the wet mixture into the dry ingredients. Stir gently until just combined; be careful not to overmix, as this can affect the cake's texture.
5. Pour into Pan: Transfer the batter to the prepared baking pan, spreading it evenly.
6. Bake: Place the pan in the preheated oven and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
7. Cool: Once baked, remove from the oven and let the cake cool in the pan for 15 minutes. Then, transfer to a wire rack to cool completely.
8. Frost (Optional): Once the cake is completely cool, you can frost it with a light orange frosting or a simple glaze made from powdered sugar and orange juice, if desired.