Preheat oven to 180 degrees celsius (or 160*c fan)
Grease a 20cm square baking tin with oil or butter and line with baking / parchment paper
Mix oil and sugar with an electric whisk or stand mixer on high for at least 2 minutes- or by hand for at least 4 minutes
Add in eggs and vanilla, whisk again until the mix is pale in colour and thickened slightly - around 3 minutes with an electric whisk or stand mixer, longer if you're doing it by hand. Stir in espresso / coffee.
Set aside a pinch of salt for later and then sift together flour, cocoa powder and salt
Add the flour mix to the wet ingredients, folding very gently until it's just combined - ie, when you can't see any dry flour or cocoa in the mix. Make sure not to over-mix.
Pour the batter into the tin, tap the base on the counter to release any air bubbles and smooth the top if needed.
Top with chocolate chunks / chips if using and sprinkle on the reserved pinch of sea salt crystals
Bake for 18-23 minutes, the sides will have cooked a bit and risen slightly and the centre of the brownie should be just set. A toothpick will come out with some mix on it for a fudgy brownie.
Allow to cool in the pan until they're room-temperature and then cut into 16 portions (or as many as you're willing to share)
Sarah
Loved this, kept us all entertained on a rainy day and tastes amazing! It’s a keeper.