Step 1: Prepare the Cake Batter: In a large mixing bowl, combine the yellow cake mix, milk, melted butter, eggs, and vanilla extract. Beat with an electric mixer on medium speed for 2-3 minutes, or until the batter is smooth and well combined. Ensure there are no lumps.
Step 2: Prepare the Baking Pan: Preheat the oven to 350F (175C). Grease and flour a 9x13 inch baking pan to prevent the cake from sticking. Alternatively, line the pan with parchment paper, leaving an overhang for easy removal.
Step 3: Assemble the Cake: Pour half of the cake batter into the prepared baking pan, spreading it evenly. Arrange half of the sliced strawberries over the batter. Gently pour the remaining batter over the strawberries, spreading it evenly. Arrange the remaining strawberries on top of the batter.
Step 4: Bake the Cake: Bake in the preheated oven for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. The top of the cake should be golden brown and slightly springy to the touch.
Step 5: Cool and Serve: Remove the cake from the oven and let it cool in the pan for 15-20 minutes before slicing. Dust with powdered sugar if desired. Serve warm or at room temperature with a dollop of whipped cream.
Tips and Substitutions: For a richer flavor, substitute melted butter with coconut oil. Gluten-free cake mix can be used to accommodate dietary restrictions. Other berries, such as blueberries or raspberries, can be used in place of strawberries. Add a streusel topping made from flour, butter, and sugar for added texture.