1Place onions, oil and butter in 3-quart microwavable casserole. Microwave uncovered on Medium-High (70%) 20 to 30 minutes, stirring occasionally, until onions are golden brown. Drain onions.
2Meanwhile, cook and drain fettuccine as directed on package. Cook bacon in 10-inch skillet over low heat, turning occasionally, until crisp; drain on paper towels. Chop bacon into small pieces.
3Heat whipping cream to boiling in 2-quart saucepan. Mix in 1 cup of the cheese and the onions. Pour over fettuccine; toss to coat. Top with remaining 1 cup cheese; sprinkle with bacon.