Mississippi Mud Cake

This recipe is taken from Sweet Serendipity by Steven Bruce.

For the 9" round cake:
2 sticks unsalted butter, softened, plus extra for the pan
1 1/2 c all purpose-flour, plus extra for the pan
1 1/2 c alkalized cocoa
2 c sugar
4 large eggs
1 c pecans, coarsely chopped
1 t vanilla extract
4 c marshmallows

For the topping:
1 1/2 c confectioners' sugar
1/2 c alkalized cocoa
1 c chopped pecans
1/2 c evaporated milk
1/2 lb (2 sticks) butter, melted and cooled

Preheat your oven to 350 degrees. Butter and flour the bottom and sides of a 9-inch round cake pan.
Sift together the flour and cocoa. Cream together the butter and sugar until fluffy. Add the eggs one at a time, beating well after each addition. At low speed, mix the dry ingredients into the butter mixture. Add the chopped pecans and the vanilla extract and continue mixing until combined.
Scrape the mixture into the prepared cake pan and bake on a rack in the middle of the oven for 25 to 30 minutes. Remove the cake and sprinkle the top with the marshmallows, then return it to the oven and continue baking until the marshmallows melt and start to brown. Remove from the oven and let cool in the pan set on a rack.
To make the chocolate-pecan topping: sift together the confectioners' sugar and the cocoa into a medium bowl. Add the pecans, evaporated milk, and melted butter, and mix until combined. Slice the cake into wedges to serve, and drizzle topping over cake as desired. Store loosely covered at room temperature.