Preheat over to 350 degrees F (approximately 180 degrees C).
Melt the chopped chocolate and butter together, either in a double boiler or in the microwave. If you're using the microwave, please be mindful not to burn the chocolate - it happens really easily and once it's got that nasty burnt taste, you can't get rid of it.
Once the chocolate and butter mixture has melted, remove it from the heat and stir it together with the sugar.
Then add in all 3 eggs, as well as the vanilla extract.
Lastly, bit by bit, stir in the flour, and finally the walnuts.
Once all the ingredients are very well combined, pour the brownie batter into a greased 13 x 9 inch (approximately 30cm x 20cm) cake pan, and bake for 35 minutes.
When you remove the brownie from the oven, it should be springy to the touch.
So, now that your brownies are cooked and springy, gently tip the baking tray over onto a cooling rack. I like to cut the brownie into squares or 'fingers' while it's still warm because I find it easier, but there's no right or wrong way. Just be careful that your friends/ family don't come along and eat pieces before you've had a chance to pack it all away!!
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Notes
Please note that the calorie content will change depending on the size of the slices you cut! I cut 6 across and 4 down, making a total of 24 pieces of chocolate brownie. On that basis, we calculated the calorific content per piece.Please also note that add-in or stir-in options (see below) will increase the calorie content of our chocolate brownies.