1. Heat the oven and ready the pan
Set the oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment for easy removal.

2. Make the batter
In a large mixing bowl, whisk the cake mix together with the eggs, sour cream, vegetable oil, and vanilla until the mixture is smooth and uniform. Avoid overworking the batter to keep the cake light.

3. Create the cinnamon-sugar layer
In a small bowl, stir the brown sugar together with the ground cinnamon until evenly combined.

4. Layer the pan
Spoon half of the cake batter into the prepared pan and spread it into an even layer. Sprinkle half of the cinnamon-sugar mixture over the batter, then scatter the diced strawberries across the surface. Pour the remaining batter over the fruit, smoothing to cover. Finish by sprinkling the remaining cinnamon-sugar evenly on top.

5. Bake
Place the pan in the oven and bake 30–35 minutes, or until a toothpick inserted near the center comes out clean or with only a few moist crumbs. Oven times vary, so check a few minutes early if your oven runs hot.

6. Make the glaze
While the cake cools slightly, whisk together the powdered sugar, milk, strawberry purée, and vanilla in a bowl until smooth. Add additional milk a teaspoon at a time if the glaze is too thick; for a tangier frosting, fold in some cream cheese.

7. Finish and serve
Let the cake rest about 10–15 minutes after coming out of the oven, then pour or spread the strawberry glaze over the warm top. Garnish with whole or sliced strawberries or a few mint leaves if you like. Allow the glaze to set slightly before slicing into squares.