Mississippi Mud Cake is typically a moist chocolate sheet cake topped with marshmallows and pecans, but this rich Bundt pan version swaps out the marshmallows and stirs in espresso and bourbon instead. It can be dusted with powdered sugar or served with an Espresso-Bourbon Caramel Sauce for an extra dose of sweet, boozy flavor.
Heat the oven to 350°F and arrange a rack in the middle. Generously coat a 12-cup Bundt pan with butter; set aside.
Place the flour, baking soda, espresso powder, and salt in a medium mixing bowl and whisk to aerate and break up any lumps; set aside.
Place the measured butter, chocolate, and brewed espresso in a medium saucepan over medium heat, stirring occasionally, until the butter and chocolate are melted and the mixture is combined (it will look curdled). Remove from the heat and stir in the granulated sugar and bourbon until smooth and the sugar has dissolved; set aside.
Place the eggs and vanilla in a large bowl and whisk until the eggs are broken up. Whisk in the chocolate mixture until smooth. Add the flour mixture and gently stir with a rubber spatula until just combined. Stir in the chocolate chips and pecans, if using.
Pour the batter into the prepared pan and bake until a cake tester or toothpick inserted into the center of the cake comes out clean, about 45 minutes.
Remove the pan to a wire rack and let the cake cool in the pan until just warm to the touch, about 45 minutes. Turn the cake out onto the wire rack and let it cool completely, at least 1 hour more. Dust with powdered sugar or serve with Espresso-Bourbon Caramel Sauce, if desired.