Make your flax eggs by combining 280ml of boiling water with your ground flaxseed. Stir well and set aside for later.
Next, make your coffee mixture by combining a teaspoon of instant coffee and a teaspoon of boiling water. Stir well and set aside for later.
Sift together flour, salt, cocoa powder and baking powder in a large mixing bowl.
In a second mixing bowl whisk together oil, sugars and flax eggs until shiny and gloopy. You want the sugar to dissolve in the oil and flax egg.
Add the vanilla essence, coffee mixture and melted chocolate (dark and milk) to your oil mixture.
Combine the dry and wet mixtures to form your brownie batter. Stir until just combined and no flour can be seen. Do not overmix.
Pour your batter into a lined square baking tin. Use a silicone spatula to even out the top a little. Top with 4-5 heaped tablespoons of peanut butter, one in each corner and one in the middle.
To create the swirls, use a skewer to draw a pattern. Stick the skewer into the brownie mixture and drag through the peanut butter topping making a figure 8 movement from left to right.
Bake for 45-50 minutes at 180°C / 356°F (fan oven setting).
Always cool the brownie in the pan fully before cutting and serving.
Notes
Make sure to use boiling hot water to make your flax eggs.
Be careful when adding instant coffee. You want it to fully dissolve in boiling hot water first, before adding to the mixture (see 'Ingredients' section and note 1 teaspoon of boiling hot water in the brackets next to instant coffee).
It’s key not to overmix this batter as doing so will create a rubber-like texture.
If you don't have a metal/wooden skewer to create swirls, you can simply use a chopstick or a thin knife.
Do notoverbake. When a wooden skewer inserted in the middle comes out clean, your brownie is way overbaked and dry. Make sure the skewer comes out gooey, with a few bits of brownie here and there.
If not using a fan oven, bake at 200°C / 392°F.
Never cut the brownie when it's still warm as it will be crumbly and very likely to fall apart.