Combine ⅔ cup flour and eggs in a bowl. Slowly stir in milk and continue mixing until combined. Set aside.
Lay your sausages across the bottom of a loaf-size baking pan. Top with 1 onion, 1 tablespoon of vegetable oil. Bake for 5 minutes at 425F.
To make the onion gravy, heat a large pan over medium and add 1 tablespoon of vegetable oil.
Add the second onion to the pan and saute until the onions are soft and slightly opaque.
Add 2 tablespoon flour, toss to coat, then add ground mustard, garlic powder, onion flakes, Worcestershire sauce, and stir in vegetable stock until everything is combined. Bring to a boil, and remove from heat.
Remove your sausages from the oven and pour the batter over. Pop the pan back in the oven for another 30 - 40 minutes.
Serve with your onion gravy, and enjoy!
Video
Notes
Choose a heavy, oven-safe pan to make your toad in a hole. Cast iron is the best option if you have one, as it ensures even cooking and a beautiful golden crust. However, any oven-safe pan will give you excellent results as well.
If you want to get a really nice sear on your sausages, preheat your pan with oil before adding the onion and sausages. You'll want to hear a lovely sizzle when you place your links in the pan.
Once you get your toad in the hole in the oven, keep the oven door closed. Resist the urge to open the door, as peeking at your toad can deflate it.
Don't overmix the batter. A few lumps are fine.
Prick the sausages to release excess fat and help them cook evenly.
Feel free to add herbs or seasonings to the batter for extra flavor.