Whisk flour, eggs, and milk into a smooth batter and season.
Rest the batter in the fridge for 24 hours.
Preheat the oven to 220°C.
Heat dripping in a pudding tray in the oven until smoking hot.
Pour batter into the tray and bake for 25 minutes.
Reduce oven to 190°C and cook for 10 more minutes.
Sauté onions and thyme in butter and oil until golden-brown.
Add garlic, sherry, and wine, and reduce by half.
Stir in flour and pour in the stock.
Simmer for 15 minutes and season with sugar and spices.
Toast baguette slices under a high grill.
Top bread with cheese and grill until melted.
Serve soup topped with croutons alongside Yorkshire puddings.