1.76 lbs (about 4 medium-sized) potatoes1 chouriço sausage (sliced)14 oz (1 can) diced tomatoes1 medium onion2 garlic clovesWhite wine, as needed1 tsp paprika3.5 oz (about 1 cup) grated cheese for gratinSalt and freshly ground pepper to tasteBéchamel sauce:1 2/3 cups (14 oz) whole milk3.5 tbsp butter1/3 cup (5 tbsp) all-purpose flourA pinch of nutmegSalt and pepper to taste