First, I followed the baking method listed here to transform my sunshine squash into puree. My squash yielded 2 cups of pumpkin puree which was twice the amount called for in the recipe, yet the muffins only vaguely tasted like pumpkin, with apple being the dominant flavor. Not quite what I was expecting for a pumpkin muffin, but still great.
I made the following substitutions from suggestions listed in the online comments:
1 1/4 cup wheat flour, 1 1/4 cup white flour
1/2 cup applesauce (instead of 1/2 cup vegetable oil)
1 cup white sugar, 1 cup brown sugar
http://allrecipes.com/Recipe/Pumpkin-Apple-Streusel-Muffins/Detail.aspx
2 1/2 cups all-purpose flour
2 cups white sugar
1 tablespoon pumpkin pie spice
1 teaspoon baking soda
1/2 teaspoon salt
2 eggs, lightly beaten
1 cup canned pumpkin puree
1/2 cup vegetable oil
2 cups peeled, cored and chopped apple
2 tablespoons all-purpose flour
1/4 cup white sugar
1/2 teaspoon ground cinnamon
4 teaspoons butter
1.Preheat oven to 350 degrees F (175 degrees C). Lightly grease 18 muffin cups or use paper liners.
2.In a large bowl, sift together 2 1/2 cups all-purpose flour, 2 cups sugar, pumpkin pie spice, baking soda and salt. In a separate bowl, mix together eggs, pumpkin and oil. Add pumpkin mixture to flour mixture; stirring just to moisten. Fold in apples. Spoon batter into prepared muffin cups.
3.In a small bowl, mix together 2 tablespoons flour, 1/4 cup sugar and 1/2 teaspoon cinnamon. Cut in butter until mixture resembles coarse crumbs. Sprinkle topping evenly over muffin batter.
4.Bake in preheated oven for 35 to 40 minutes, or until a toothpick inserted into a muffin comes out clean.
