Preheat the oven to 180*C/350*F/ gasoline mark 4. Butter a 9 inch flan pan with a removeable backside effectively after which put aside.
Whisk collectively the flour, sugar, cocoa powder, baking powder and salt in a bowl. Beat collectively the butter, eggs and vanilla. Add to the dry components and blend till clean. Stir within the toasted nuts. Pour into the ready pan. Bake on a center shelf of the oven for 25 to half-hour, or till a toothpick inserted within the centre comes out clear. Instantly sprinkle the marshmallows on high and return to the oven for a couple of minutes to soften the marshmallows. Take away from the oven and punctiliously unfold the chocolate frosting over high.
To make the chocolate frosting combine all components collectively in a bowl, beating with an eletric whisk till clean and thick. Unfold on the new marshmallows.
Let cool utterly. Minimize into wedges to serve.