Grease and line your 23cm length X 10cm width X 10cm height (9 X 4 X 4 inch) steel Pullman pan. Mine is USA Pan brand in size small.
Whisk the dry ingredients together in a large, non reactive (plastic or glass) mixing bowl.
Whisk the wet ingredients into the dry, ensuring you get all the flour off the bottom of the bowl. The mixture should be nearly liquid at first, but thicken to a loose batter consistency as you whisk.
Cover the bowl and set aside for 1 hour to proof. After proofing, the dough should have visible signs of aeration - a puffy top, lots of little air bubbles inside, etc.
Preheat your oven to 220C/428F. This bread can proof quickly, so I recommend preheating the oven early if you are baking in a humid or hot climate (where high hydration bread proofs more quickly). Remove the top rack in the oven if your oven is small.
Once the dough is proofed, decant it into your greased and lined Pullman pan. Use a moist hand to smooth down the top of the loaf, then cover the pan thoroughly without touching the bread. I use an inverted produce bag which keeps the bread in a sealed environment without touching it as it proofs.
The loaf is proofed once it domes over the top of the Pullman pan. This can take as little as 20-30 minutes in a hot environment or up to 2 hours in a cold environment. Make sure you check on your loaf so that it doesn't over proof.
When it is ready, place the bread in the oven for 20-30 minutes. Sorghum bread tends to be quite pale, so this time is to encourage oven spring but also browning.
After 20-30 minutes, turn the oven down to 200C/400F and continue to bake for an additional 20 minutes for a total baking time of 40-50 minutes. The loaf should be golden brown on top and feel solid if you tap the top of the loaf.
Allow the bread to cool in the pan for 15 minutes before transferring it onto a wire rack to cool. For best results, allow it to cool completely before slicing (the next day or 3+ hours after baking is ideal).
Slices keep well in an airtight container in the fridge or can be frozen and defrosted.