Preheat the oven to 350°F (175°C) and grease a 9×13-inch pan. A properly heated oven helps the cake rise evenly.

Whisk together flour, baking powder, and salt in a large bowl until evenly combined. Set aside.

In another bowl, beat butter and sugar on medium speed until light and fluffy. This step adds air for a soft texture.

Add eggs one at a time, mixing well after each addition, then stir in vanilla. The mixture should look smooth and slightly creamy.

Add the dry ingredients, then pour in the milk. Mix on medium speed just until a soft, fluffy batter forms with minimal lumps. Do not overmix.

Spread the batter evenly into the prepared pan and smooth the top gently.

Bake for about 25 minutes, checking at 20 minutes. The top should be lightly golden, and a toothpick inserted in the center should come out clean.

Let the cake cool completely in the pan before frosting to prevent melting.

Spread icing over the cooled cake and finish with sprinkles if desired.