Prepare Oven and Pan: Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish thoroughly.

Make Cake Batter: In a large bowl, combine yellow cake mix, vegetable oil, eggs, and sour cream. Mix until smooth and well blended.

Combine Cinnamon Swirl: In a separate small bowl, mix brown sugar and cinnamon until evenly combined.

Layer Batter and Swirl: Pour half of the cake batter into the prepared pan. Evenly sprinkle the cinnamon and brown sugar mixture over the batter, then drizzle strawberry jam on top. Pour the remaining batter over the jam layer. Using a knife or skewer, gently swirl the layers to create a marbled effect.

Bake: Place in the oven and bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean and the cake turns golden brown. Remove and let cool slightly.

Prepare Icing: While the cake cools, whisk together powdered sugar, strawberry puree, milk, and vanilla extract until smooth. Adjust milk quantity for desired drizzle consistency.

Serve: Drizzle the strawberry cream icing generously over the warm cake. Slice and serve immediately.