1) Preheat the oven to 230C/Gas 8.
2) Mix the flour with the salt. In a small bowl or mixing cup, mix the treacle with 425ml water and crumble in the yeast.
3) Sit the bowl for a few minutes in a warm place to allow the yeast to start to work. Grease a 13-by-20cm loaf tin with sunflower oil. Meanwhile, check to see if the yeast is rising. After about 4-5 minutes it will have a creamy and slightly frothy appearance on top.
4) When ready, stir and pour it, with all the remaining 275ml water, into the flour to make a loose, wet dough. The mixture should be too wet to knead. Put the mixture into the greased tin. Sprinkle the top of the loaf with sesame seeds, if you like. Put the tin in a warm place somewhere close to the cooker or near a radiator perhaps. Cover the tin with a tea towel to prevent a skin from forming. Just as the bread comes to the top of the tin, remove the tea towel and pop the loaves in the oven for 20 minutes, then turn the oven down to 200C/Gas 6 for another 40-50 minutes, or until it looks nicely browned and sounds hollow when tapped. The bread will rise a little further in the oven. This is called 'oven spring'. If, however, the bread rises to the top of the tin before it goes into the oven it will continue to rise and flow over the edges.
We usually remove the loaves from the tins about 10 minutes before the end of cooking and put them back into the oven to crisp all round, but if you like a softer crust there's no need to do this.