Preheat oven to 350 degrees F. Grease a 9x13-inch baking dish.
In a medium mixing bowl using a hand mixer, beat together cake mix, 1 egg, and 1/2 cup butter. Press the mixture into greased baking dish.
In a medium mixing bowl using a hand mixer, beat together cream cheese, 1/2 cup melted butter, 3 eggs, vanilla, and powdered sugar. Mix until completely smooth. Stir in the diced strawberries.
Spread the cream cheese mixture over the crust. Bake uncovered for 45 minutes. Do not over-bake. The center should still be slightly jiggly.
Cool completely. Sprinkle slightly cooled bars with powdered sugar, if desired. (Highly recommend it!)