Preheat your oven to 400° F
In your mixing bowl, whisk together the dry Crispy Batter Mix and 1/2 teaspoon of thyme. Then add the milk, eggs, Dijon mustard, and Worcestershire sauce. Whisk until the mixture is smooth. Put the batter mixture in your refrigerator until you are ready to use it
Heat a tablespoon of olive oil in your large frying pan over medium heat. Add your leeks to the frying pan and cook them, stirring frequently, for 5-8 minutes. They should be nicely colored at the edges. Add 1 teaspoon thyme, salt, and pepper just before you finish cooking the leeks. Put the leeks in a bowl and set aside
Put your 9" by 13" baking pan in the 400° oven for 5 minutes. Remove the pan, place the sausages in it, and then put it back in the oven for 10 minutes, until the sausages are not quite cooked and only slightly browned. Remove the sausages from the pan and put on a plate
Pour the refrigerated batter mix into the hot pan
Scatter the leeks over the batter, then scatter the sausages, and then the rest of the thyme.
Put your Toad in a Hole in the oven and cook for 25-30 minutes, until the batter is even and golden
While your Toad in a Hole is baking, prepare the onion gravy