Preheat your oven to 350F. Grease a 8 by 8 baking pan and set aside. You may use a larger 9 by 9 pan, but of course your brownies will be thinner.
Melt the butter and the unsweetened chocolate in a medium pan over low heat. Remove from heat, add the sugar and beat well.
Add your eggs one at a time, beating well after each egg. The chocolate mixture will get glossy.
In a small bowl mix together your flour, salt, and baking powder, to distribute the baking powder evenly. Add to the chocolate mixture.
Add the walnuts and mix until just combined. Quickly pour into your baking pan, and smooth the top.
Bake for 20- 25 minutes. These brownies are meant to be chewy. It is better to underbake these brownies than to overbake them, 25 minutes should be all the time they need. When done they should be solid but the top will spring back up when you press on it lightly.
Let cool thoroughly before adding the icing.
Chocolate Buttercream Icing Recipe
In the bowl of a stand mixer with an icing attachment add the butter. Whisk on high speed for a minute, scrape down the sides of the bowl, and whip the butter for another minute, until the butter is a light yellow colour.
Before adding any dry ingredients stop the mixer, proceed on low speed, once incorporated speed up the mixer. This will significantly reduce the mess from the cocoa and icing sugar.
Stop the mixer and add the cocoa, beat on low speed until incorporated, then beat on high for a minute. Again scrape down the sides of the bowl.
Stop the mixer and add half the icing sugar. Start it on low until incorporated, then beat on high for a minute. Taste your icing and decide if its fine as is. If you like the icing sweet continue with using the rest of the icing sugar. If you want to cut the sweetness, replace 1/2 cup of the icing sugar with flour. Then beat until smooth and fluffy.
Crunchy Cookie Topping
Take 8 cookies of your choice. I used chocolate girl guide cookies, Oreos, Fudgee-o would be perfect as well. Simply chop the cookies into large chunks, spread over the fresh icing and press them down to hold.