Ingredients
For the cake
1 cup (240 ml) strong hot espresso
1 cup (227 g) unsalted butter
½ cup (50 g) unsweetened cocoa powder
2 cups (400 g) white sugar
2 cups (250 g) all-purpose flour
1 teaspoon baking soda
½ teaspoon baking powder
½ teaspoon salt
2 large eggs
½ cup (120 ml) sour cream
1 tablespoon vanilla extract
For the gooey mud topping
2 cups (260 g) mini marshmallows
½ cup (115 g) unsalted butter
¼ cup (25 g) cocoa powder
⅓ cup (80 ml) strong espresso
2 cups (250 g) powdered sugar, sifted
1 teaspoon vanilla extract
Instructions
Begin by warming your kitchen with the soft aroma of fresh espresso—brewed strong, almost smoky—because that will become the heart of this mud cake. In a saucepan, melt the butter gently with the espresso and cocoa powder, letting them swirl together into a dark, glossy pool. As the mixture warms, stir in the sugar until it dissolves like evening light fading into dusk.
Set this mixture aside to cool slightly, then reach for a large bowl. The flour, baking soda, baking powder, and salt come together first, forming a soft, pale cloud. Pour the warm espresso-cocoa mixture into it, and the aroma deepens as everything folds together. Crack in the eggs, add the sour cream and vanilla, and the batter becomes velvety—thick, rich, and unmistakably indulgent.
Spread this luscious batter into your pan and slide it into the oven. As it bakes, the whole space begins smelling like a chocolate espresso shop tucked away on a rainy street. When the cake is just set, still tender in the middle, remove it and let it rest for a moment.
While it’s warm, scatter mini marshmallows over the top so they slowly soften and slump into the heat. Meanwhile, in a small saucepan, melt the butter with cocoa and espresso again, creating a silky glaze. Stir in the powdered sugar and vanilla until smooth, then pour this warm chocolate-espresso river over the marshmallows. It melts them further, creating that signature “mud”—gooey, shiny, and irresistible.
Let the cake settle just enough to slice, though it’s best when still a little warm, with the marshmallow mud stretching softly as you lift each piece.