Cut squash in half lengthwise; discard seeds and membrane. Place squash, cut sides down, on a baking sheet coated with cooking spray; bake at 400° for 55 minutes or until tender. Cool slightly. Scoop out squash pulp from skins; discard skins. Mash pulp.
Preheat oven to 325°.
Place sugar and butter in a large bowl; beat with a mixer at medium speed until blended. Add eggs, 1 at a time; beat after each addition. Add squash and juice; beat until combined.
Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour and remaining ingredients in a medium bowl; stir with a whisk. Add flour mixture to squash mixture; beat until just combined. Spoon about 1/3 cup batter into each of 12 (6-ounce) ramekins coated with cooking spray. Place 6 ramekins in each of 2 (13 x 9-inch) baking dishes. Add hot water to pans to a depth of 1 inch. Cover pans loosely with heavy-duty foil coated with cooking spray.
Bake at 325° for 22 minutes or until a wooden pick inserted in center comes out clean. Cool completely on a wire rack. Serve with Vanilla Jack Sabayon.