Preheat oven to 350 degrees F. Line sixteen 2 1/2-inch muffin cups with paper bake cups; set aside. In a medium bowl combine all-purpose flour, white whole wheat flour, baking powder, cinnamon, curry powder, salt, and cayenne pepper (if using); set aside.
In a large bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add brown sugar; beat until combined. Add squash, ginger, egg, and vanilla; beat until combined. Alternately add the flour mixture and soy milk to squash mixture, beating on low speed after each addition just until combined.
Spoon batter into prepared muffin cups, filling each about two-thirds full.
Bake in the preheated ove about 20 minutes or until muffin tops spring back when lightly touched. Cool in muffin cups on a wire rack for 5 minutes. Remove from muffin cups. If desired, sprinkle lightly with powdered sugar. Serve warm.