Remove butter, eggs, cream cheese, and Cool Whip from the fridge. Allow to come to room temperature for at least 30–60 minutes. Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish with non-stick spray or butter.
In a large mixing bowl, beat the softened butter and granulated sugar together on medium speed for 2–3 minutes until pale and fluffy. Add the eggs one at a time, mixing briefly after each. Mix in the baking powder and salt.
Add the flour and milk in alternating additions — start with one-third of the flour, mix gently, then half the milk, and repeat. Always start and end with flour. Stir in the vanilla extract. Do not overmix once the flour is added.
Pour the batter into the prepared pan and spread into an even layer. Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean. The cake should look flat and light-colored, not golden or domed.
Remove the cake from the oven and allow it to cool completely on a wire rack — at least 45 minutes to 1 hour. Do not add frosting to a warm cake.
Beat the softened cream cheese in a large bowl until completely smooth with no lumps. Add the sifted powdered sugar and beat again until silky. Taste and add more powdered sugar if desired.
Gently fold the thawed Cool Whip into the cream cheese mixture using a rubber spatula. Use slow fold-and-turn motions to preserve the airiness. The frosting should be light and fluffy.
Spread the cream cheese frosting evenly over the cooled cake, working from the center outward. Cover loosely with plastic wrap and refrigerate for at least 3 hours, or overnight.
Just before serving, hull and slice the fresh strawberries and arrange them in an even layer over the chilled frosting. Slice into bars and serve immediately.