Preheat the oven to Bake 400°F. Line the baking pan with aluminum foil. In the lined pan, toss the bread cubes with 4 tablespoons of olive oil, cheese, thyme, ½ teaspoon salt and ¼ teaspoon white pepper. Bake the croutons until crispy and browned, about 15 minutes. Remove pan from oven. Transfer croutons on foil to a cooling rack.
Set the oven to Roast 400°F. In the baking pan, toss fennel, leek and potato with remaining 2 tablespoons olive oil and 1 teaspoon kosher salt. Roast the vegetables until softened and starting to brown, 30-35 minutes.
Add broth, cream, wine, vinegar, remaining ½ teaspoon salt and ¼ teaspoon white pepper to blender in the order listed. Add roasted vegetables. Select the Soup setting and press start. Once the cycle finishes, pour soup into serving bowls. Chop reserved fennel fronds. Sprinkle on soup and top with croutons.