1. In a large skillet over medium-high heat, melt butter. Add the onions, pepper flakes and salt; saute until onions are tender. Stir in garlic. Reduce heat to medium-low; cook, stirring occasionally, for 30-40 minutes or until the onions are deep golden brown.
2. Add the grape tomatoes, vinegar and 2 tbsp. oil to the skillet. Cook pasta according to package directions. Drain pasta; toss with onion mixture.
3. Drizzle with remaining olive oil. Sprinkle with bacon, Parmesan cheese and pepper, and heat through. Garnish with fresh basil if desired.
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