Preheat the oven to 180c. I use a square, silicone cake tray so it doesn't need greasing but I would suggest that for a metal cake tin you line with greaseproof paper. It also makes it easier to get out of the tin before slicing!
In a large saucepan, melt the dark chocolate, margarine, sugar, honey and milk over a low heat. Make sure you stir it to prevent the chocolate burning or you'll end up with a very stodgy mess!
Remove from the heat and stir in the vegetable oil. Set this chocolate melty mix aside to cool while you weigh out the 'dry' ingredients into your large mixing bowl or stand mixer.
With the stand mixer on minimum, drizzle in the chocolate mixture and stir on low, scraping down the sides and bottom, until completely combined!
Scoop the whole lot into the prepared tin and bake at 180C for 25minutes until the top has a lovely crust but the inside is still really squidy.
If they are for later, leave to set in the fridge before slicing, or eat them like Daddy Peacock - scooped warm on top of a big bowl of ice-cream!