Heat oven to 350°F Line large rimmed baking sheet with foil, spray with nonstick cooking spray. Generously butter 10 1/2 cup nonstick muffing cups. Cut squash in half; rmove seeds. Place cut side down, on baking sheet. Bake 40 minutes until almost tender.
Turn squash cut side up, sprinkle with brown sugar and butter. Bake 30-35 minutes or until tender.
Scoop flesh of squash with butter sugar mixture into a large bowl (should have about 4 cups). With a potato masher, mash squash until smooth. Stir in remaining ingredients until well combined.
Fill muffin cups with squash mixture.
Note: Custards can be made to this point up to 1 day ahead. Cover and refrigerate. An additional 5-10 minutes baking time may be needed.
Bake 30-35 minutes or until brown around edges and toothpick inserted in center comes out moist but not wet.
Cool in pan 5 minutes, invert onto baking sheet. With spatula, gently place custards on serving platter.