Start by preheating your oven to 450 degrees Fahrenheit. In a bowl, sift together the self-rising flour, salt, and rubbed sage. Mix in the large egg, then slowly whisk in the milk until you have a smooth, creamy batter. Set this aside to rest for 1 hour.
While the batter rests, prick the pork sausages all over with a fork. Grill them lightly or brown them in a frying pan until they've taken on some color. In a Yorkshire pudding dish or pie pan, add about 4 tablespoonfuls of pan drippings and place it in the preheated oven until the fat is spitting hot.
Once the fat is ready, quickly stir 1 tablespoon of the hot fat into your batter. Immediately arrange the browned sausages in the pan with the remaining hot fat, then pour the batter over the top. You need to work very fast here so the batter hits the fat while it's still hot enough to brown around the edges of the pan as soon as it's poured in.