Warm the milk in a small saucepan until it bubbles, then remove from heat. Mix in the sugar, stirring until dissolved. Let it cool until it's lukewarm.
In a small bowl, dissolve the yeast in warm water. Let stand until creamy, about 10 minutes.
In a large bowl, combine the milk, yeast mixture, butter and 1/2 of the flour. Beat until smooth. Add salt and rest of flour, or enough to make a soft dough. Knead. Place in greased bowl, cover, and let rise.
Knock back. Roll out to about 1/2 cm thick. Cut rounds with a plain cutter or glass. Sprinkle a baking tray or greaseproof paper with polenta and put the rounds on this to rise. Dust the tops of muffins with polenta also. Cover and rise 30 minutes.
Heat a greased heavy frying pan or griddle. Cook muffins on griddle about 10 minutes on each side on medium heat. Keep baked muffins in a warm oven until all have been cooked. To use, split and toast.