This is the recipe I made to take:
Katherine Hepburn Brownies
1/2 cup (1 stick) butter
1 oz unsweetened chocolate
1 tsp pure vanilla extract
3/4 cup flour
1 cup sugar
2 large eggs, slightly beaten
1/4 tsp salt
1/2 cup walnuts, chopped (I used pecans)
a handful of Mini-marshmallows
Position rack in the middle of the oven and preheat to 325 F. Butter and flour an 8" square baking pan.
In a mixing bowl mix together sugar, eggs, and vanilla, whisk until well blended. In another bowl combine flour and salt.
Melt butter and chocolate in a double boiler, stirring until smooth. Add in a stream to the egg mixture whisking constantly so you don't make scrambled eggs. Stir in the flour just until blended. Add the nuts. Transfer the mixture to the prepared baking pan.
Bake for 35-40 minutes or until a wooden pick inserted in the center comes out sticky with just a few crumbs clinging to it but is not wet. Do Not Overbake. The edges start to pull away from the sides of the pan as well.
Remove the pan from the oven and add the mini marshmallows to the top of the brownies and put back into the oven, just until they begin to melt. Do Not Brown. (I used a large spreader and spread the marshmallows as soon as the pan is removed from the oven into an even layer so I could spread the frosting over the top. This step is totally optional.)
Let cool for 5-10 minutes and spread or drizzle fudge frosting over the top.
Fudge Frosting/Glaze
3/4 of a stick of butter (6 Tbsp)
1 1/2-2 Tbsp cocoa powder
3 Tbsp milk (I used evaporated milk since I had left over)
1/2 tsp vanilla
1/2 lb powdered sugar
Melt the butter in a small saucepan over medium low heat. Add the cocoa powder and stir until smooth. Add the milk, vanilla and powdered sugar. Whisk until very smooth.
This frosting is quite thin, if you want it thicker, simply add more powdered sugar.
The original recipe was found at one of my favorite blogs Get Off Your Butt and Bake:
