1. Preheat oven to 400°. Melt butter with oil in a large skillet over medium-high heat. Add onions, sugar, and salt; cook, stirring occasionally, 8 minutes or until onions soften and just begin to turn golden. Reduce heat to medium, and cook, stirring often, 20 minutes or until onions turn deep golden brown. Stir in vinegar, scraping bottom of skillet to deglaze pan. Cook, stirring often, until vinegar is reduced by half. Stir in thyme.
2. Cook bacon in a large skillet over medium-high heat 8 to 10 minutes or until crisp. Drain on paper towels; finely crumble.
3. Combine cheese and next 3 ingredients in a medium bowl. Stir in onions and bacon. Transfer to a 2-cup baking dish.
4. Bake 20 minutes or until mixture bubbles and top is lightly golden.