1. In a large nonstick skillet, heat oil over medium-high heat. Add onion and cook, stirring frequently, until golden, about 15 minutes. Cover and reduce heat to medium-low. Cook, stirring occasionally, until golden brown, 35 to 40 minutes. Cool slightly, then coarsely chop.
2. In a medium bowl, stir together cream cheese and sour cream until smooth. Reserve 2 tablespoons bacon; stir remaining bacon, the onion, vinegar, thyme, salt and pepper into cream cheese mixture. Chill at least 30 minutes. (Can be stored in an airtight container in the refrigerator up to 2 days.) Sprinkle with reserved bacon and garnish with thyme sprigs, if desired. Makes 2 cups.