Mississippi Mud Cake

Preparation - Preheat the oven to 350°F. Arrange a rack in the center of the oven. Lightly spray a 9x13-inch metal baking pan with nonstick cooking spray.

Batter - Make the batter: In a large bowl, whisk together the hot coffee and cocoa powder until smooth. Let sit to bloom (this helps develop the chocolate flavors) and cool slightly, about 5 minutes.

Batter - Add the remaining ingredients: Add the sour cream, melted butter, oil, eggs, and vanilla to the coffee mixture and whisk until smooth. Add the granulated sugar and whisk to combine. Add the flour, baking powder, baking soda, and salt and whisk until just combined.

Baking - Bake the cake: Scrape the batter into the prepared pan. Bake the cake until risen and a toothpick inserted into the center comes out clean, 25 to 30 minutes. Don't turn off the oven.

Topping - Top with the marshmallows and pecans: Remove the cake from the oven. Sprinkle the mini marshmallows evenly over the cake. There will be gaps between the marshmallows—that's okay. Return the cake to the oven and bake until the marshmallows are just puffed and some of their definition is lost, closing the gaps, about 2 minutes. Set the pan on a wire rack. Top the marshmallow layer evenly with 1 cup of the chopped pecans and reserve the remaining 1/3 cup (if using).

Icing - Make the icing: Immediately after topping the cake with pecans, make the icing. Add the butter to a medium saucepan and melt over medium heat. Add the cocoa powder, milk, vanilla, and salt to the butter and whisk until smooth. Gradually whisk in the powdered sugar until smooth and glossy. Remove from the heat and let cool ever so slightly, 2 to 3 minutes.

Finishing and Storage - Finish the cake: Give the icing a good stir and then pour it evenly over the cake. Take the time to pour the icing evenly as it's a bit difficult to spread with a spatula after the fact. Top with the remaining 1/3 cup of pecans (if using). Allow the cake to cool completely in the pan set over the wire rack before serving. Use a sharp knife lightly sprayed with nonstick cooking spray to slice the cake (this helps to keep the marshmallow from sticking to the knife). Leftover cake can be stored in an airtight container or in the pan tightly wrapped with plastic wrap at room temperature for up to 4 days. Freeze in an airtight container for up to 3 months.