Cream the Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy. This should take about 3-4 minutes using an electric mixer on medium speed.
Add the Eggs and Vanilla: Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Mix in the vanilla extract.
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the butter mixture, alternating with the milk. Begin and end with the dry ingredients. Mix until just combined, being careful not to overmix.
Bake the Cake: Pour the batter into the prepared baking pan and smooth the top with a spatula. Bake for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Cool the Cake: Allow the cake to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely before frosting.
Preparing the Frosting
Cream the Butter: In a large bowl, beat the softened butter until creamy and smooth.
Add Powdered Sugar and Milk: Gradually add the powdered sugar, 1/2 cup at a time, beating on low speed until combined. Add the milk and vanilla extract, and beat on medium-high speed until the frosting is light and fluffy.
Frost the Cake: Once the cake is completely cool, spread the frosting evenly over the top using a spatula. You can also use a piping bag for a more decorative finish.