1. Sauté first 3 ingredients in hot oil in a Dutch oven over medium heat 5 minutes. Add navy beans and next 3 ingredients, and cook, stirring often, 2 to 3 minutes. Add broth, and bring to a boil; reduce heat to low, and simmer, stirring occasionally, 20 to 30 minutes. Remove from heat; let stand 10 minutes.
2. Transfer about 4 cups potato mixture to a food processor or blender using a slotted spoon. Process 30 seconds or until smooth, stopping to scrape down sides. Return pureed mixture to Dutch oven, stirring until blended. Stir in yogurt; season with pepper to taste. Serve warm or cold. Store in refrigerator up to 1 week.