Whisk flour, eggs, and milk into a smooth batter and refrigerate overnight.
Preheat the oven to 220°C.
Brown the sausages in a frying pan with olive oil.
Melt beef dripping in a roasting tin in the oven and whisk thyme and seasoning into the batter.
Place sausages in the hot tin, pour over batter, and bake for 35-40 minutes.
Open the oven door to release steam, reduce heat to 180°C, and bake for 10 minutes.
Sauté onions in butter until soft for the gravy.
Stir in gravy granules, yeast extract, and vegetable stock, then boil and simmer for 5 minutes.
Season the gravy and stir in a final knob of butter before serving over the toad-in-the-hole.