5-Ingredient Key Lime Dump Cake

Key lime dump cake takes everything you love about key lime pie — the bright, tangy filling and the buttery crumb — and turns it into a dessert that barely involves any effort. You layer a few ingredients right in the baking dish, pop it in the oven, and out comes a dessert with a tart custard base and a golden, cookie-like top.

It’s the kind of recipe you scribble on a scrap of paper because it feels like a hack. Five ingredients, no mixing bowls, and it still tastes like summer.

Why This One Stays in the Rotation

The sharp lime custard cuts through the richness of the cake mix topping, so you get both bright and indulgent in every bite. It’s my go-to when I need a last-minute dessert that doesn’t look like it came from a box.

I’ve made it with regular limes when key limes aren’t around, and it still delivers. The real magic is how the condensed milk thickens into a silky layer beneath the crisp topping without you lifting a whisk.

Ingredients

• 1 (14 oz) can sweetened condensed milk: this creates the creamy, tangy base.
• ½ cup fresh key lime juice: bottled juice works if fresh isn’t available.
• 2 teaspoons lime zest: from about 2 limes, use only the green outer peel.
• 1 (15.25 oz) box white cake mix: just the dry mix, no added ingredients.
• ½ cup (1 stick) melted unsalted butter: melted, not softened.

Variations / Substitutions

• Swap for regular limes: Persian limes are a fine substitute. Add 1 tablespoon extra sugar to the condensed milk to mimic key lime sweetness.
• Add cream cheese cubes: scatter 4 oz of cold cream cheese cut into small chunks over the filling before topping for a creamy bite.
• Go lemon: replace lime juice and zest with lemon, and you have a lemon dump cake.
• Add coconut: sprinkle ½ cup sweetened shredded coconut over the cake mix before the butter.

For a berry twist, try our Blueberry Lemon Dump Cake.

How to Make 5-Ingredient Key Lime Dump Cake

Step 1: Mix the Lime Filling

Preheat your oven to 350°F (175°C). In a 9×13-inch baking dish, pour the 1 can of sweetened condensed milk, add the ½ cup key lime juice and 2 teaspoons lime zest, and whisk with a fork until smooth and evenly combined. No need to grease the dish; the filling won’t stick.

The mixture will look thin and pale yellow with tiny flecks of green. Whisk for about 30 seconds until the zest is dispersed and no streaks of milk remain.

Step 2: Layer the Topping

Sprinkle the entire box of dry white cake mix evenly over the lime mixture, breaking up any large clumps with your fingers. Then slowly pour the melted ½ cup butter over the dry mix, trying to cover as much of the surface as possible. Some dry spots are okay; they’ll turn into crispy bits.

The butter will pool in places and soak into the cake mix. Don’t stir — just let it sit. That separation is what creates the crisp cookie-like top and the soft, moist layer underneath.

Step 3: Scoop and Serve

Bake for 40 to 45 minutes, until the topping is deeply golden and the filling is bubbling around the edges. The center should look set but still jiggle slightly when you shake the pan. Let it cool for at least 15 minutes before serving to allow the lime layer to firm up.

Scoop generous spoonfuls into bowls, making sure to get both the creamy custard and the buttery crumble. A dollop of whipped cream and a pinch of lime zest on top will make it feel like you spent hours on it.

A Few Notes Before You Start

• Use a glass baking dish if you can.: It conducts heat evenly and lets you see when the edges start bubbling, a sign the custard is set.
• Zest before you juice.: It’s much easier to pull the bright green zest from whole limes, and the pith beneath is bitter, so stop once you hit white.
• Cool it for clean layers.: Right out of the oven, the layers are loose. After a 15-minute rest, you’ll get distinct spoonfuls of custard and crumble.

Bake times shift slightly depending on your dish. Check a few minutes early if using metal.

Storing Leftovers

• Refrigerate: in an airtight container for up to 4 days. The topping will soften slightly, but the tangy flavor gets even better cold.
• Reheating: is optional — a brief 20-second zap in the microwave returns some of the warmth while leaving the custard silky.
• Serve cold: straight from the fridge on a hot day. It’s almost like a key lime pie bar.

Frequently Asked Questions

Why did some of my cake mix stay powdery?

The dry mix wasn’t fully coated with butter. Next time, cut the ½ cup stick of butter into thin pats and place them close together over the whole surface instead of pouring melted butter.

Can I use a different flavor cake mix?

Yes, a yellow or lemon cake mix works beautifully. The lemon one boosts the citrus even more.

Can I make this gluten-free?

Sure. Swap the white cake mix for a gluten-free vanilla cake mix. No other changes needed.

What if I don’t have key limes?

Regular Persian limes work without fuss. The filling will be slightly less floral but still bright and delicious.

Key Lime Dump Cake Recipe

Print Recipe Pin Recipe

Prep Time 5 minutes mins

Cook Time 45 minutes mins

Total Time 50 minutes mins

Servings: 8 servings

Calories: 450

Ingredients Method Notes

Ingredients

  

• 1 (14 oz) can sweetened condensed milk
• ½ cup fresh key lime juice
• 2 teaspoons lime zest
• 1 (15.25 oz) box white cake mix
• ½ cup (1 stick) melted unsalted butter

Method

 

1. Preheat oven to 350°F (175°C). Whisk condensed milk, lime juice, and zest directly in a 9×13-inch dish until smooth.
2. Sprinkle dry cake mix evenly over the filling, then slowly pour melted butter over the top without stirring.
3. Bake 40-45 minutes until golden and bubbly. Cool 15 minutes, then scoop into bowls and serve with whipped cream and extra zest.

Notes

The dry cake mix will look patchy and powdery before baking — that’s normal. During the 15-minute cool, the custard firms up enough to hold its shape when you scoop. If you want neat squares, chill the whole dish for an hour instead.