In the mixing bowl of a kitchenaid mixer, dissolve the yeast and sugar in warm water. Allow to stand for 5 minutes.
Add the milk, butter, brown sugar, squash, and salt. Stir to combine.
Gradually add the white whole wheat flour. Mix the dough on medium speed for 2 minutes. Stir in enough bread flour to form a soft dough ball.
Turn the dough out onto a floured surface. Knead until smooth and elastic.
Place the dough in a bowl coated with olive oil, turning once to coat top. Cover with plastic wrap and let rise in a warm place until doubled, about 1 hour.
Punch the dough down and turn onto a floured surface. Divide into 16 portions. Place in a 9x13 glass baking dish coated with nonstick cooking spray. Cover and let rise until doubled, about 45 minutes.
Bake at 400 degrees 13 minutes or until golden brown. Remove from pans to wire racks to cool.
