Saute onion in reserved hot drippings over medium heat for 10 minutes or until tender and lightly browned. Remove from heat; cool.
Process onion, buttermilk, sour cream, ranch dressing mix, basil and garlic cloves in food processor until smooth, stopping to scrape down sides.
Top each lettuce wedge with dressing; sprinkle with bacon. Top with additional shredded basil if desired.
NOTE: You can make the dressing ahead of time and store in refrigerator. This recipe take more time to make the dressing from scratch, but it's well worth it.