Preheat the oven to 220°C/gas mark 7. Lightly whisk the eggs in a jug along with the herbs and milk. Mix the flour and baking powder together in a large bowl. Make a well in the centre and pour in the wet ingredients, whisking all the time. Season, then set aside for at least 20 minutes.
10 minutes before you're ready to cook, spritz a square baking dish (roughly 20x20cm) with the olive oil spray and put in the oven to heat up. Carefully remove the hot dish from the oven and add the sausages. Cook for 10 minutes or until golden brown.
Remove from the oven and pour over the batter. Return immediately to the oven and cook for 20-25 minutes until the batter is puffed up and golden brown and the sausages are cooked through.
Meanwhile, make the gravy. Combine the stock with the juniper berries and set aside.
Lightly spray a non-stick frying pan with the olive oil, then cook the sliced onions for 8-10 minutes until golden brown and slightly sticky. Add the garlic and cook for another minute.
Stir in the flour to form a paste. Remove the juniper berries from the stock and then pour in slowly, stirring all the time to make a gravy. Serve alongside the toad in the hole and cooked peas.