Heat the oven to 230°C (450°F), Gas Mark 8.
Put the mushrooms, stalk side up, in a large, shallow ovenproof dish.
Melt the butter with 4 tablespoons of the oil in a frying pan. Add the garlic and herbs and a little salt and pepper and stir for about 30 seconds. Pour the sauce over the mushrooms and bake in the oven for 2 minutes.
Meanwhile, put the flour in a bowl and slowly whisk in the eggs, horseradish sauce, milk and a little salt and pepper until really smooth.
Pour the batter over the mushrooms and return to the oven for 20–25 minutes, until the batter has risen and is golden.
Heat the rest of the oil in a frying pan. Add the onions and sugar and fry for 10 minutes until deep golden, stir in the flour, then pour in the beer and stock and add a sprinkling of salt and pepper. Stir for 5 minutes.
Cut up the toad and pour the beer gravy generously over the top of each serving.