In a large bowl, dissolve yeast in 1/2 cup warm water. Stir in 1 teaspoon sugar; let stand for 5 minutes. Add the squash, milk powder, oil, salt, 2 cups flour and remaining water and sugar; beat until smooth. Add enough remaining flour to form a soft dough. Cover and let rest for 10 minutes.
Turn dough onto a floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch dough down; turn onto a floured surface. Roll to 1-in. thickness. Cut with a 2-1/2-in. biscuit cutter. Place in a greased 13-in. x 9-in. baking pan. Cover and let rise until doubled, about 30 minutes.
Bake at 375° for 20 -25 minutes or until golden brown. Cool on a wire rack. Brush with butter.