Preheat your oven to 350°F (175°C) to ensure even baking.

In a greased 9x13" dish, pour in the melted butter and spread it evenly. Sprinkle brown sugar over the butter, then layer drained pineapple slices on top.

In a bowl, combine the yellow cake mix with crushed pineapple and its juice (no water needed). Stir until smooth, then pour the batter over the pineapple layer.

Bake for 35–40 minutes, until golden brown and a toothpick inserted in the center comes out clean. Let the cake cool completely before adding the topping.

Whisk vanilla pudding mix with cold milk until thickened, then fold in whipped topping for a light, fluffy texture.

Once the cake is cool, either frost the top or slice it horizontally and add the creamy filling in the middle.