Ingredients
1 (15.25-ounce) box yellow cake mix (standard size, no pudding added)
2 (20-ounce) cans crushed pineapple in juice, undrained
1/2 cup unsalted butter, melted (1 stick)
Directions
Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with aluminum foil, letting it overhang the sides for easy lifting later, and lightly grease the foil with a thin film of butter or nonstick spray.
In a large mixing bowl, pour in the dry yellow cake mix. Do not prepare it according to the box; you are using the dry mix only.
Add both cans of crushed pineapple with all of their juice directly to the bowl with the cake mix. The pineapple juice replaces the liquid and eggs you would normally add.
Stir the cake mix and pineapple together with a spatula or wooden spoon until you have a thick, evenly moistened batter. It will look slightly lumpy from the fruit, but you should see no dry pockets of mix.
Pour the thick pineapple batter into the prepared foil-lined pan and spread it into an even layer, nudging it into the corners with your spatula.
Drizzle the melted butter evenly over the top of the batter, letting it naturally pool and streak across the surface. This helps create those rich, caramelized golden edges and a moist crumb.
Place the pan on the center rack of the preheated oven and bake for 35 to 45 minutes, or until the top is deep golden brown, the edges are caramelized, and a toothpick inserted in the center comes out with just a few moist crumbs (no wet batter). Ovens vary, so begin checking around 30 minutes.
Remove the pan from the oven and set it on a wire rack to cool. Let the cake cool at least 20 to 30 minutes in the pan so it can set; it will slice more cleanly but will still be soft and moist.
Use the foil overhang to gently lift the cooled cake from the pan, if desired, or simply leave it in the tray for serving. Cut into squares and serve warm or at room temperature, straight from the foil-lined pan for that casual, family-style feel.
Variations & Tips
You can play with this basic 3-ingredient framework without losing its easy charm. For a slightly tangier flavor, replace one can of crushed pineapple with a 20-ounce can of pineapple tidbits and chop them lightly before adding; this gives a mix of texture in the crumb. A teaspoon of vanilla extract or a pinch of ground cinnamon stirred into the batter complements the pineapple nicely, though it technically nudges you past three ingredients. If you prefer a less rich cake, you can reduce the melted butter to 1/3 cup; the cake will still be moist from the pineapple juice but the edges will be a bit less caramelized. For a more pronounced buttery, almost cobbler-like top, increase the butter to 3/4 cup and watch closely so the edges don’t overbrown. You can also bake this in two 8-inch square pans for smaller gatherings; start checking for doneness around 25 to 30 minutes. Food safety-wise, store leftovers tightly covered in the refrigerator after the cake has fully cooled, since the high moisture from the pineapple can encourage spoilage if left out too long; it will keep well for about 3 days. Reheat individual squares briefly in the microwave to bring back that just-baked softness. Always make sure canned pineapple is used before its expiration date, and discard any can that is dented, bulging, or rusted to avoid contamination.