Step 1

Halve and thinly slice 1 small yellow onion. Crush 6 garlic cloves.

Step 2

Empty 1 (28-ounce) can whole peeled tomatoes and their juices into a large Dutch oven or other heavy pot with a lid. Add the onion, garlic, 2 cups water, 4 tablespoons unsalted butter, 2 tablespoons rice flour, 2 tablespoons tomato paste, 1 tablespoon Italian seasoning, 2 1/2 teaspoons kosher salt, 2 teaspoons granulated sugar, 1 teaspoon fennel seeds, and 1/2 to 1 teaspoon red pepper flakes. Stir to combine, then cover and bring to a simmer over medium-low heat. Simmer, stirring halfway through, until onions are soft and translucent and the liquid has thickened slightly, 15 to 18 minutes total.

Step 3

Remove pot from the heat and add 1/2 cup heavy cream. Working in batches if needed, transfer the soup to a blender and blend until smooth, 2 to 3 minutes. Transfer to a large bowl. (Alternatively, purée the smooth directly in the pot with an immersion blender.)

Step 4

Rinse out the Dutch oven and return the bisque to the pot. Taste and season wiith more kosher salt and/or granulated sugar as needed. Cover and keep warm over low heat while making the croutons.

Step 5

Arrange an oven rack 5 inches away from the broiler element; heat the broiler to LOW. Using a serrated knife, cut 1/2 medium baguette crosswise into 8 slices (about 3/4-inch thick). Place the baguette rounds on a rimmed baking sheet and broil until slightly dried out on top, 1 to 2 minutes.

Step 6

Remove from the oven. Slice 4 ounces Brie cheese into 8 wedges. Place a wedge of cheese on each baguette slice. Return to the oven and broil until cheese is slightly melted and blistered in spots, 2 to 3 minutes more.

Step 7

Ladle the bisque into 4 bowls. Top each bowl with 2 of the toasted Brie croutons and freshly ground black pepper if desired.