Preheat the oven to 350°F (175°C).

In a mixing bowl, combine the softened butter and granulated sugar. Beat until light and fluffy.

Add eggs one at a time, mixing well after each. Pour in the vanilla extract and blend until incorporated.

In a separate bowl, whisk together flour, baking powder, and salt.

Gradually add the dry mixture to the wet ingredients, mixing until just combined.

Grease the baking pan to prevent sticking.

Pour the batter into the prepared pan and smooth the top.

Bake for 20 minutes or until a toothpick comes out clean.