Preheat the Oven: Start by preheating your oven to 350°F (175°C) and greasing a 9x13-inch baking pan.
Mix the Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
Cream Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3-5 minutes.
Add Eggs: One at a time, add the eggs to the butter and sugar mixture, mixing well after each addition.
Incorporate the Milk: Gradually add the milk to the mixture, followed by the lemon and orange zest.
Combine Dry and Wet Ingredients: Slowly add your flour mixture to the wet ingredients, mixing until just combined. Avoid overmixing!
Bake: Pour the batter into the greased baking pan and smooth the top. Bake for 30 minutes or until a toothpick inserted in the center comes out clean.
Prepare the Glaze: While the cake is baking, whisk together the powdered sugar, lemon juice, and orange juice until smooth.
Cool and Glaze: Once the cake is done, allow it to cool in the pan for about 10 minutes. Then, invert it onto a wire rack and let it cool completely before drizzling the glaze over the top.