Preheat the oven to 180C (160C fan forced)
Grease a 16cm x 23cm tin or disposable aluminium container.
Place the chocolate and butter in a heatproof bowl.
Place the bowl over a saucepan of gently simmering water and stir gently to melt the butter and chocolate together. Set aside to cool slightly whilst you are preparing the remainder of the ingredients.
Sift together the spelt, cocoa powder and salt. Set aside.
Combine the Guinness and
vanilla extract and set aside.
Weigh the sugar into the bowl of a stand mixer.
Add the eggs to the sugar and beat on high speed until the mixture is thick and creamy. This will take approximately 3-4 minutes.
With the mixer on low speed, drizzle in the chocolate mixture and beat until just combined.
Add 1/3 of the Guinness and mix until just combined.
Add half of the sifted flour and cocoa, again mixing until just combined.
Repeat with 1/3 of the Guinness and the remainder of the flour. Finish by mixing in the remaining 1/3 of the Guinness.
Pour the mixture into your lined tin and bake for 25 - 30 minutes, until the top is set and a skewer inserted in the middle comes out with only a few crumbs adhering to it.
Allow to cool completely in the tin before cutting.