Preheat oven to 350 [degrees] F. Wash, halve, and remove seeds from squash. Cut a 1-inch-thick slice off one of the squash halves; set aside. Place squash halves, cut sides down, in a baking dish. Bake for 50 to 55 minutes or until tender. Remove pulp from squash; discard shells. Measure 1 cup.
Place the 1 cup of squash in a medium saucepan. Add the 1 1/2 cups milk, the sugar, 2 tablespoons butter, and salt. Heat and stir just until warm (120 [degrees] F to 130 [degrees] F). Set aside.
In a large mixing bowl combine 2 cups of the flour, the yeast, and sage. Add the squash mixture. Beat with an electric mixer on low to medium speed for 30 seconds, scraping sides of the bowl. Beat on high speed for 3 minutes. Stir in as much of the remaining flour as you can, using a wooden spoon.
Turn the dough out onto a lightly floured surface. Knead in enough of the remaining flour to make a moderately stiff dough that is smooth and elastic (6 to 8 minutes). Shape dough into a ball. Place dough in a lightly greased bowl, turning once to grease surface of the dough. Cover and let rise in a warm place until double in size (45 to 60 minutes).
Punch dough down. Turn dough onto a lightly floured surface. Divide dough in half. Cover; let rest for 10 minutes. Meanwhile, lightly grease two 8x4x2-inch loaf pans.
Gently shape each portion into a loaf, tucking edges under. Place the shaped dough in the prepared loaf pans. Cover and let rise in a warm place until nearly double in size (about 30 minutes).
Preheat oven to 375 [degrees] F. Use a vegetable peeler to make several thin strips from the reserved 1-inch slice of squash. Brush surface of bread with milk. Place squash strips on top of loaf. Brush squash strips with the melted butter.
Bake about 35 minutes or until bread sounds hollow when you tap the top with your fingers. (If necessary, cover loosely with foil the last 15 minutes of baking to prevent overbrowning.) Immediately remove bread from pans. Cool on wire racks. Makes 2 loaves (32 servings).