In the bowl of a stand mixer or another large mixing bowl combine warm milk, eggs, yeast, sugar, warm melted butter, salt, sour cream and vanilla. Add 480g/4 cups flour to make a batter consistency of sour cream. Cover with a cling wrap and a towel and let it rise in a warm place for 2 hours.
Add 600g/5 more cups of flour; one cup at a time or until the dough no longer sticks to your hands to make a very soft and elastic dough. Stir in chocolate chips or raisins, candied citrus peel or nuts. (Anything you like in your sweet bread). Cover and let dough rise another 2 hours in a warm place. The rising process will take longer if your house is not very warm.
Divide dough evenly into three deep 8" baking pans, that have been well-oiled. Try not to handle the dough too much. Let dough rise uncovered in a warm place for additional 2 hours or until you see a significant rise.
Bake at 350F/180C for 35-40 minutes or until golden. Remove from the pan and cook on a wire rack.
Once the loaves are at room temperature, melt white chocolate in a double boiler over low heat and cover the tops of bread with it. Use sprinkles to decorate.