Heat 1 tablespoon of olive oil over medium-high heat in a large Dutch oven.
Add the sausage and cook, breaking it up as it cooks, until no longer pink. Remove the sausage with a slotted spoon and transfer it to a large bowl
Add the remaining tablespoon of olive oil to the pot. Add the onion, carrot, celery, red pepper flakes, and salt and pepper.
Cook over medium heat for 7 to 8 minutes, stirring occasionally, until the vegetables soften and begin to take on color.
Add the garlic and cook for 1 minute, stirring constantly. Transfer the cooked vegetables to the bowl with the sausage.
Add the Swiss chard to the pot and cook for 2 to 3 minutes, just until wilted. Season with additional salt and freshly ground black pepper to taste. Transfer the greens to the bowl with the sausage and vegetables. Set aside.
Reduce the heat to medium-low and melt the butter in the pot. Whisk in the flour and cook for 2 minutes, stirring constantly to form a smooth roux.
Slowly whisk in 1 1/2 cups of the stock, a little at a time, until smooth and thickened. Add the remaining stock and bring to a gentle boil. Reduce the heat and simmer for 10 minutes, stirring occasionally.
Stir in the white beans and the reserved sausage and vegetable mixture. Simmer gently for 5 to 10 minutes, until heated through and well combined. Taste and add salt and pepper, if needed.