Warm the milk in a small saucepan until it bubbles then remove from heat. Mix in the sugar, stirring until dissolved. Let cool until lukewarm. In a small bowl dissolve yeast in warm water. Let stand until creamy, about 10 minutes.
In a large bowl combine the milk, yeast mixture, copha and 3 cups 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.
Punch down. Roll out to about 1cm thick. Cut rounds with biscuit cutter, drinking glass or empty tuna can. Sprinkle waxed paper with polenta and set the rounds on this to rise. Dust tops of muffins with polenta also. Cover and let rise 1/2 hour.
Heat greased 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. Allow to cool and place in plastic bags for storage. To use, split and toast.