1. In a large saucepan, melt butter over medium heat. Add onions and garlic and cook, stirring, until tender but not browned, about 8 minutes. Add potatoes, season with salt and pepper and cook, stirring occasionally, for 5 minutes. Pour in broth; bring to a boil over high heat, then reduce heat to low, cover and simmer until potatoes are very soft, about 25 minutes.
2. Remove from heat and let cool slightly. Add half-and-half and 3/4 cup Gorgonzola and stir until cheese has melted. Working in batches, puree soup in a blender until smooth. Rinse out saucepan, wipe dry and return soup to it. Gently rewarm soup over medium-low heat; do not boil. Season with salt and pepper. Ladle into bowls and garnish with chives and remaining 2 Tbsp. Gorgonzola.