Place water and polenta in a small saucepan. Bring to the boil over medium heat, stirring occasionally. Cook until mixture thickens; about 5 minutes. Remove from heat and stir in the butter and treacle. Let cool to lukewarm.
In a small mixing bowl, dissolve yeast in warm water. Let sit until creamy; about 10 minutes.
In a large mixing bowl, combine the cooled polenta mixture with the yeast mixture; stir until well blended. Add about half the flour and the salt; mix well. Add the remaining flour, a little at a time, stirring well after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 8 minutes.
Lightly oil a large mixing bowl, place the dough in the bowl and turn to coat with oil. Cover with a damp cloth and put in a warm place to rise until doubled in volume, about 1 hour.
Preheat oven to 190 C / Gas mark 5.
Deflate the dough and turn it out onto a lightly floured surface and form into a loaf. Place the loaf in a lightly greased 23x12cm (9x5 in) loaf tin. Cover with a damp cloth and let rise until doubled in volume, about 40 minutes.
Bake in preheated oven for about 30 minutes or until the top is golden brown and the bottom of the loaf sounds hollow when tapped.