For the sponge: mix the sugar, yeast, and flour together in bowl. Pour in the warm milk. Beat until smooth, then cover with plastic wrap and set aside for 1/2 hour. Add the eggs, salt, sugar, and one cup of the flour to the sponge. Beat until smooth. Then add the butter in small chunks and beat well. Add the remaining flour a handful at a time and mix in until a soft but kneadable dough is achieved and the butter thoroughly incorporated. Knead the dough by hand or with a mixer until it is smooth and satiny, about 5 minutes. Place the dough in a greased bowl, cover with plastic wrap, and let rise and room temperature until doubled in size, 1 1/2 to 2 hours. Deflate the dough, recover the bowl, and refrigerate overnight. The next day, make the fillings before shaping the loaves. Blueberry Filling: combine all of the ingredients in a small saucepan and bring to a boil over medium heat while stirring constantly. Reduce heat and simmer for 5 minutes, then remove from heat and let cool. Egg Glaze: combine the egg and milk in a bowl and beat until combined. Cream Cheese Filling: combine all the ingredients in a bowl and mix until combined Once your filling has cooled off, take the dough out of the refrigerator and gently deflate it. Divide it into two pieces. Use a rolling pin to shape each piece into a thin (1 cm.) rectangle. Spread your fillings in the center of the dough. At an angle, slice the sides of the dough into tabs approximately 1 inch wide. Alternating from side to side, fold the pieces in over the filling. When possible, gentle press on the tabs to seal the folds. After it has been fully folded, glaze the braid with egg wash. Cover loosely with plastic (I place the entire baking pan in a clean kitchen garbage bag). Set aside to rise until doubled in size, approximately 45 minutes. While it is rising, preheat the oven to 350. Just before placing the braid in the oven, glaze it again with any remaining egg wash. Bake on the center rack of the oven for approximately 35 to 40 minutes, rotating it once after 20 minutes so that it bakes evenly. Remove it from the oven and allow it to cool for at least half an hour before slicing.