Another Mary Berry recipe: Chocolate Brownies!

Inspired by the success of the last Mary Berry recipe I used I decided to have a stab at another. Unfortunately this wasn't as successful as the result was more of a cakey brownie. I really like gooey brownies- and these weren't. However for a good chocolate cake style brownie they are good. And also fairly easy to make.
I had a helping hand from my boyfriend, Tom, on the decorating side, with a rather innovative topping of Kit Kat Chunky, fudge pieces and raspberry sugar.
When making the frosting be careful on the amount of water you use.

Here's the recipe:

Ingredients:
225g butter
350g light muscovado sugar
4 large eggs
50g cocoa powder, sifted
250g self-raising flour
85g walnut pieces (optional) I didn't use these

For the frosting:
25g unsalted butter (room temp), cubed
3 tbsp cocoa powder, sifted
225g icing sugar, sifted

1.Preheat the own to 180 degrees C (fan 160/350 F/ Gas 4). Grease a traybake tin measuring 30cm x 25cm and 4cm deep and line the base of the tin with baking parchment.
2. Place the butter, sugar, eggs, cocoa powder and flour in a large bowl. Beat with an electric mixer on a low speed for about 3 minutes, or with a wooden spoon for a little longer, until smooth. Stir in the walnut pieces, if using.
3. Spoon the mixture into the tin, spread evenly, then bake for 40-45 minutes, covering with foil for the last 10 minutes.

4. Test for doneness by inserting a skewer in the centre- if it comes out clean then the brownies are ready. Leave to cool slightly in the tin, then turn out on a wire rack to cool completely.

5. Make the frosting in a bowl, soften the butter and add the cocoa powder. Gradually stir in 4 tablespoons of boiling water until smooth, then stir in the icing sugar. Leave the frosting to cool before icing the brownies.

6. Spread the frosting evenly over the brownie base with a palette knife. Leave to set then cut into squares.