Melt the butter in a large saucepan over medium heat and add the flour. Cook, whisking, until the mixture is smooth and thick, about 2 minutes. Add the leeks and tasso and cook, stirring often, for 3 minutes.
Slowly add the stock, whisking, and simmer for 10 minutes. Add the cream and simmer for about 5 minutes. Season to taste with salt, pepper, and Tabasco. Serve warm in soup bowls.