CUT calabaza into chunks. Steam or boil in large saucepan on medium-high heat until tender, about 25 minutes. Drain; place back in saucepan and set aside.
HEAT olive oil in large skillet on medium heat. Add tomato and onion, cook until soft. Add cooked tomato mixture to calabaza. In two batches, place cooked calabaza and tomato mixture in blender container or food processor; cover. Blend until smooth.
PLACE mixture back into large saucepan. Stir in evaporated milk, sugar, nutmeg, salt and pepper; mix well. Cook over medium heat, stirring occasionally, until just boiling. Serve in soup bowls with a sprinkle of cinnamon and a dollop of sour cream.