Step 1: Preheat and Prepare. Preheat your oven to 350°F (175°C) and grease your 9x9-inch baking dish or line it with parchment paper.
Step 2: Make the Cake Base. In a large mixing bowl, combine the cake mix, melted butter, and egg. Stir until well combined.
Step 3: Assemble the Base. Spread the cake batter evenly into the prepared baking dish, pressing it down gently.
Step 4: Add the Raspberries. Evenly distribute the raspberries over the cake batter, gently pressing them in.
Step 5: Prepare the Gooey Filling. In a separate bowl, combine the condensed milk, white chocolate chips, brown sugar, flour, and cinnamon. Mix until smooth and pour over raspberries.
Step 6: Make the Topping. Combine cold butter pieces with remaining cake mix, brown sugar, and cinnamon to create a crumbly topping. Sprinkle over the filling.
Step 7: Bake. Bake for about 30-35 minutes, until golden brown and a toothpick comes out clean.
Step 8: Cool and Slice. Allow to cool for 15 minutes in the pan, then transfer to a wire rack to cool completely before slicing.
