Adjust rack to top position and preheat oven to 425 degrees. (TIP: If you have a toaster oven, feel free to skip preheating.) Wash and dry all produce. Peel and dice sweet potato into ½-inch pieces. Halve, peel, and finely dice onion. Remove and discard any large stems from kale. Place 2 TBSP butter (4 TBSP for 4 servings) and a pinch of Italian Seasoning (you’ll use the rest later) in a small microwave-safe bowl; bring to room temperature.

Heat a large drizzle of olive oil in a large pot over medium-high heat. Add onion and cook, stirring occasionally, until softened, 4-5 minutes. Add sausage and cook, breaking up meat into pieces, until browned and cooked through, 4-6 minutes.

Stir sweet potato, stock concentrates, remaining Italian Seasoning, 2½ cups water (5 cups for 4 servings), and a big pinch of salt into pot. Cover and bring to a boil. Once boiling, reduce heat to medium and simmer, covered, for 7 minutes.

Once soup has simmered for 7 minutes, uncover pot and stir in kale. Simmer, uncovered, until kale has wilted and sweet potato is tender, 5-7 minutes. Season generously with salt and pepper.

Meanwhile, mix softened butter and Italian Seasoning until thoroughly combined. Season with salt. (TIP: If butter is not yet softened, microwave for 5-10 seconds.) Halve baguette; spread herb butter onto cut sides. Toast on top rack (or in a toaster oven) until golden, 3-5 minutes. Halve each baguette piece on a diagonal.

Divide soup between bowls and top with Parmesan and a pinch of chili flakes if desired. Serve with toasts on the side.