Preheat the oven to 350ºF. Grease and flour a 9-inch springform pan with non-stick cooking spray. Set aside.
In a large mixing bowl, beat together melted butter, granulated sugar, and brown sugar. Then, add eggs and vanilla extract. Beat until combined.
In another bowl, whisk together flour, cocoa powder, baking powder, and salt. Add to the wet ingredients. Stir using a rubber spatula until smooth. Then, gently fold in pecans and chocolate chips.
Transfer the batter to the prepared springform pan. Bake in the preheated oven for 25-30 minutes. Check the readiness with a toothpick inserted in the center, if it comes out clean - the fudge brownie pie is ready.
While the fudge brownie pie is baking, prepare the chocolate frosting. In a bowl, whisk together the melted butter, cocoa powder, evaporated milk, vanilla extract, and powdered sugar until smooth
When the pie is ready, remove it from the oven and top with mini marshmallows. Return to the oven and broil for 30 seconds to 1 minute or until marshmallows are puffed and slightly golden. Keep an eye on them, they can burn easily. Remove from the oven.
Top with the chocolate frosting. Let the pie cool before slicing. Enjoy!