Place the lukewarm water in a measuring cup, sprinkle with the yeast, and set aside for 5-10 minutes.  In a small bowl, combine the butter and sugar, beating until smooth and pale yellow.  Set aside.  In a large mixing bowl, add flour and salt.  With the mixer running add, milk mixture, yeast and eggs.  Mix until dough comes together.  Add butter/sugar mixture 2 tablespoons at a time.  Mixing well after each addition.  Continue to mix for 3-5 minutes or until the dough is smooth and elastic.  form the dough into a ball and place in a buttered bowl.  cover and allow to rise for 1 3/4 hours.  Punch the dough down and reshape into a smooth ball.  Return to bowl and cover with plastic wrap and refrigerate overnight.

The next day, remove the dough from the refrigerator and let stand in the bowl at room temperature for 1 hour.  Then divide the dough into 12 4-ounce (113 g) portions.  Shape into round balls.  And place in buttered brioche tins or flattened muffin paper liners.  Cover with a cloth and allow to rise for 1 1/2  - 2 hours or until dough feels like a marshmallow when gently pressed.

After dough has risen, mix egg yolk and milk together.  Gently brush the tops with egg wash and sprinkle generously with pear sugar.  Place in a 350 degree F (176C) oven for 18-20 minutes or until deep golden brown.  Remove from tins and place on a cooling rack.