Heat oven to 400°F. Scrub potatoes clean; prick each a few times with fork. Bake directly on rack in center of oven 60 to 70 minutes or until tender. Cool 10 minutes. Increase oven temperature to 450°F. Cut each potato in half; scrape potatoes out of skins into bowl, leaving 1/4-inch shell. Mash potatoes with fork or potato masher. Set aside. Brush shells, inside and out, with melted butter; sprinkle with salt. Cut each shell in half lengthwise, and then into 1/2-inch strips crosswise. Place on cookie sheet; bake about 20 minutes or until golden and crispy. Set aside. Meanwhile, in 4-quart Dutch oven, cook bacon over medium-high heat until crisp. Remove bacon with slotted spoon; set aside. Decrease heat to medium. Add onion. Cook 3 to 4 minutes, stirring occasionally, until tender. Add 3 tablespoons of the flour, the thyme leaves and pepper; cook 1 to 2 minutes, stirring occasionally. Beat in chicken stock and mashed potatoes with whisk; heat to boiling. Reduce heat to low; simmer 30 minutes. Stir in cream; heat to simmering. In medium bowl, toss 1 1/2 cups of the cheese with remaining 1 tablespoon flour. Add cheese mixture, 1/2 cup at a time, until cheese is melted and soup is smooth after each addition. To serve, ladle soup into serving bowls. Garnish with remaining cheese, sour cream, green onions, bacon and crispy potato skins.