To make the candied peanuts, put the peanuts on the lined baking sheet with the golden syrup and a pinch of salt. Pop in the oven while it’s heating up. After 10 minutes, give them a stir with a spatula, then return to the oven and cook for a further 10 minutes, or until the golden syrup starts to become really sticky and darkens in colour. Once done, take out of the oven (but leave the oven on) and separate out the peanuts so they aren’t all clumped together. Set aside to cool.
Meanwhile, melt the chocolate in a bain-marie, then add the oil and leave to warm and merge evenly. Pour into a large mixing bowl or the bowl of your stand mixer, but leave the bain-marie on the heat with the water in the pan still simmering. Add the sugar to the chocolate and oil mixture and combine.
In the same bowl you used for the bain-marie, mix together the cornflour (cornstarch) and cold water. Once they’re combined, add the boiling water, then place the bowl back on the simmering pan to heat up as you stir. The mixture will thicken. Add this cornflour mixture to the chocolate and sugar bowl and mix until glossy and fully emulsified. If the mixture splits, add a splash of boiling water to bring it together. Now add the ground almonds, oat flour, cocoa powder and salt, then mix to combine.
Pour the mixture into the other lined tray and spread to the corners so it’s level. Fill the piping bag with the peanut butter and snip a 5mm hole in the end. Use it to pipe patterns of your fancy across the brownie. If you don’t have a piping bag, just dollop the peanut butter on top. You can swirl it in with a toothpick to make pretty patterns. Sprinkle the candied peanuts over the top and bake for 40-45 minutes. You’ll know it’s ready when the top becomes firm, but the brownie still has a little jiggle in it.
Best eaten once cooled. This will keep for a week in an airtight container in the fridge.