Mississippi mud pie bars are a decadent, no-fuss twist on the classic Southern chocolate dessert. A buttery cookie crust is topped with a fudgy brownie layer, a gooey marshmallow topping, and a glossy chocolate ganache. They’re perfect for potlucks, parties, or whenever you need a serious chocolate fix—and they come together with simple ingredients in about an hour.
Ingredients
- For the crust: 1 ½ cups (190 g) all-purpose flour, ½ cup (100 g) granulated sugar, ½ cup (115 g) unsalted butter, cold and cubed, ¼ teaspoon salt
- For the brownie layer: ½ cup (115 g) unsalted butter, melted, 1 cup (200 g) granulated sugar, 2 large eggs, 1 teaspoon vanilla extract, ⅓ cup (40 g) unsweetened cocoa powder, ½ cup (65 g) all-purpose flour, ¼ teaspoon salt
- For the marshmallow topping: 2 cups (120 g) mini marshmallows (about half a 10-oz bag)
- For the ganache: 1 cup (240 ml) heavy cream, 1 ½ cups (255 g) semisweet chocolate chips or chopped chocolate
Instructions
- Preheat your oven to 350°F (175°C). Line a 9×9-inch (23×23 cm) baking pan with parchment paper, leaving overhang on two sides for easy lifting.
- Make the crust: In a medium bowl, whisk together the flour, sugar, and salt. Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Press the mixture evenly into the bottom of the prepared pan. Bake for 12–15 minutes, until lightly golden. Set aside to cool slightly while you make the brownie layer.
- Make the brownie layer: In a large bowl, whisk the melted butter and sugar together until smooth. Add the eggs one at a time, whisking well after each, then stir in the vanilla. Sift in the cocoa powder, flour, and salt, and stir until just combined—do not overmix.
- Pour the brownie batter over the warm crust and spread it evenly. Bake for 20–25 minutes, until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). The brownie layer should be set but still fudgy.
- Remove the pan from the oven and immediately sprinkle the mini marshmallows evenly over the hot brownie layer. Return to the oven for 2–3 minutes, just until the marshmallows begin to puff and soften—do not let them brown completely. Remove and set aside to cool for about 15 minutes.
- Make the ganache: In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer (small bubbles around the edges). Remove from heat and pour over the chocolate chips in a bowl. Let stand for 2 minutes, then stir slowly until smooth and glossy.
- Pour the ganache over the marshmallow layer, spreading it gently to cover. Let the bars cool completely at room temperature, about 30 minutes, then refrigerate for at least 1 hour to set the ganache and make slicing easier.
- Lift the bars out using the parchment overhang, place on a cutting board, and slice into 16 squares with a sharp knife. Wipe the knife clean between cuts for neat edges.
Tips
- Don’t overbake the brownie layer. The bars should be fudgy, not cakey. Start checking at 20 minutes—the toothpick should come out with a few moist crumbs, not clean.
- Use full-fat cream for the ganache. Low-fat or half-and-half can make the ganache runny. If you don’t have heavy cream, you can substitute ½ cup whole milk plus ½ cup butter (still 1 cup total liquid), but the ganache will be slightly less firm.
- Chill before slicing. At least 1 hour in the fridge helps the ganache set and makes clean cuts. If the bars are too cold, let them sit at room temperature for 5 minutes before slicing.
- Substitute the marshmallows. If you don’t have mini marshmallows, you can use 1 ½ cups of marshmallow creme (like Fluff) spread over the hot brownie layer—it won’t puff as much, but it will still be gooey.
Serving Suggestions
Serve these bars at room temperature for the fudgiest texture, or slightly chilled for a firmer bite. They pair beautifully with a scoop of vanilla ice cream, a drizzle of caramel sauce, or a dollop of whipped cream. For a boozy adult twist, add a splash of bourbon or Kahlúa to the ganache—just remember to serve responsibly.
Variations
- Peanut butter mud pie bars: Swirl ½ cup (130 g) creamy peanut butter into the brownie batter before baking, and use peanut butter chips in the ganache.
- Mint chocolate version: Add ½ teaspoon peppermint extract to the brownie batter and top with a mint-chocolate ganache (use mint chocolate chips).
- Gluten-free: Substitute the all-purpose flour in both crust and brownie with a 1:1 gluten-free baking flour blend. The texture will be slightly crumblier but still delicious.
- Extra crunchy: Sprinkle ½ cup chopped pecans or walnuts over the marshmallow layer before adding the ganache.
Storage and Reheating
Store leftover bars in an airtight container in the refrigerator for up to 4 days. They can also be frozen for up to 3 months—wrap individual bars in plastic wrap and place in a freezer-safe bag. Thaw in the refrigerator overnight or at room temperature for 30 minutes. To reheat, microwave a single bar for 10–15 seconds to soften the ganache and marshmallow, or warm in a 300°F (150°C) oven for 5–7 minutes.
Frequently Asked Questions
Can I use a pre-made brownie mix? Yes, you can substitute a 9×9-inch brownie mix for the homemade brownie layer. Prepare the mix according to the package directions, but reduce the baking time by 2–3 minutes since the crust adds to the total bake time.
Why did my ganache turn out grainy? Grainy ganache usually happens when the chocolate seizes—often due to a drop of water or overheating. To fix it, add a tablespoon of warm cream and stir gently. If it’s still grainy, it’s still usable; just spread it as is.
Can I make these bars ahead of time? Absolutely. They actually taste better the next day once the flavors meld. Prepare them up to 2 days ahead, keep them refrigerated, and slice just before serving.
Can I use milk chocolate instead of semisweet? Yes, but the ganache will be sweeter and softer. If you use milk chocolate, reduce the cream to ¾ cup (180 ml) to keep the ganache firm enough to slice.
How do I get clean slices? Use a sharp knife and wipe it with a damp paper towel between cuts. For even cleaner edges, dip the knife in hot water and dry it before slicing.
Can I skip the crust? You can, but the bars will be very rich and gooey. If you skip the crust, reduce the brownie layer baking time by 3–5 minutes and expect a denser, more fudge-like texture.
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