7 tablespoons unsalted butter
2 medium fennel bulbs, cleaned and thinly sliced, fronds chopped and reserved
1 large onion, halved, peeled and thinly sliced
2 teaspoons coarse kosher salt
4 garlic cloves, finely chopped
½ teaspoon chile powder
3 tablespoons Pernod
2 28-ounce packages or cans chopped tomatoes packed in purée (such as Pomì)
1 cup chicken stock
1 teaspoon black pepper
6 baguette slices
1 teaspoon fennel seeds
3 ounces Brie, thinly sliced
Melt 6 tablespoons butter in a large pot over medium heat. Add fennel, onion and 1/2 teaspoon salt. Toss to combine. Reduce heat to medium-low. Partly cover and cook, stirring occasionally, until vegetables are very tender, about 20 minutes. Stir in garlic and chile powder; cook 1 minute. Stir in Pernod and cook until almost completely evaporated, about 3 minutes.
Pour in tomatoes, 1 1/2 cups water and the stock. Bring to a simmer and cook gently, uncovered, for 30 minutes. Season with 1 1/2 teaspoons salt and the black pepper. Purée soup in batches using a blender or immersion blender until smooth.
Transfer soup back to pot over medium heat; simmer until slightly thickened, 5 to 10 minutes more. Scrape down sides and bottom of pot occasionally. Remove from heat and cover to keep warm.
Heat oven to 350 degrees. Spread bread slices on a large baking sheet. Bake until light golden, about 10 minutes.
Toast fennel seeds in a small skillet over medium heat until fragrant and lightly colored, 2 to 3 minutes. Melt in remaining 1 tablespoon butter.
Adjust oven temperature to broil and position rack 6 inches from heat. Brush toasts with fennel-seed butter and top with Brie. Return to oven and broil until bubbly and golden, 1 to 3 minutes (check every minute or so to see that they are not burning). Ladle soup into bowls and top with a cheese crouton. Garnish with fennel fronds.