Add the remaining 1 tablespoon of the butter to the pan and let it melt. Add the andouille and cook, stirring often, until much of the fat has rendered and the andouille is crisp, about 3 minutes. Add the onion to the pan and sauté, stirring often, for 2 minutes. Add the garlic, shallots, and scallions and cook for 1 minute. Add the tomatoes, cook for 1 minute, then raise the heat to high and add the shrimp stock. Simmer, stirring occasionally, until most of the liquid has evaporated, about 5 minutes. Add the sour cream to the pan and stir to combine. Return the shrimp to the pan, gently folding them into the liquid, and heat just until the shrimp are cooked through, about 3 minutes.