
Ingredients
254 g of butter (1 + 1/4 cups)
112 g of cocoa powder (1 cup and a small spoon or smth)
200 g of dark brown sugar (just under 1 cup)
100 g of granulated sugar (1/2 cup)
4 eggs and 1 egg yolk
140 g of plain flour (1 + 1/6 cups)
(optional) few drops of vanilla extract
200 g of choc chips (around 1 + 1/4 cups)
Cake tin I used was a square one with a side length of 25cm
Preparation
First thing: you want to melt 254 g of butter and leave it on medium heat until it turns a slightly dark golden brown color. Then you want to add that to 112 g of cocoa powder and mix until they are combined, and it should look very dark. In a separate bowl, add 4 eggs and an egg yolk, and add 200 g of dark brown sugar and 100 g of white sugar (for a sweeter taste, add 50 g more of sugar).
Whisk that together for around 4–5 minutes. Add the choc + butter mixture to the other bowl with the sugar and eggs, and stir with a spatula. At this stage, you could use a mixer or whisk, but it's up to you. Measure 140 g of plain flour and sift that in. I would recommend not using an electric whisk at this point. If you prefer a less fudgy brownie, I would add a few spoons extra of flour. Add chocolate chips to the mix or roughly chop a 100 g bar of milk chocolate and a 100 g bar of dark chocolate — so that's 200 g in total — and add that to the mix instead of the chocolate chips.
(I coated my choc chunks in a little bit of flour before mixing them into the batter because apparently, that way they don't just sink to the bottom of the tin). At this point, you might want to add a few drops of vanilla extract, but it's optional.
I don't preheat the oven, and that does affect the baking time a bit, but turn your oven to gas mark 3 or 4, which is around 160°C / 180°C-ish. Put the batter into the tin and then place the tin into the oven and bake for around 25–30 mins-ish. If it's not done after 30 mins, keep it in for around 5 mins more. Afterwards, keep it warm but make sure to turn the oven off.
Note: before placing the pan in the oven, I sprinkled some cocoa powder over the top.
Let it rest for around 30 minutes, then cut it into pieces and enjoy.