Melt the butter in a large saucepan, add the onions, stir through and cover directly with a piece of parchment paper or foil – a cartouche. Keep the heat low so they don’t colour and cook until soft, stirring occasionally – about 20 minutes.
Once soft, add the potatoes, leeks, garlic, thyme, bay leaf and pepper and stir together. Pour in the milk and stock, bring to the boil then reduce the heat to a simmer and cook until the potatoes are soft. Stir in the cream.
Remove the sprigs of thyme and the bay leaf. Using a hand blender, blitz the ingredients to form a smooth, velvety soup.
To make the bacon crumble, place the slices of bacon on a baking sheet lined with foil, top with another sheet of foil and then another baking sheet to weight the bacon down.
This will increase the temperature inside and the bacon will turn nice and crispy. Pop in the oven for 20-25 minutes at 200°C/180°C Fan/Gas 6. Remove from the baking sheet and drain on kitchen paper, it will crisp up as it cools. Chop the bacon and mix with the parsley and toasted breadcrumbs.
Serve the soup in warmed bowls and top with the bacon and parsley crumb.
Try this soup with a lovely mushroom and truffle caviar. Fry 100g finely chopped little portobello mushrooms in 15g butter until
soft, stir in 1 dessertspoon of finely chopped reconstituted porcini, a sprinkle of sea salt and white pepper.
Finish with 1 teaspoon of truffle oil, a tablespoon of toasted breadcrumbs and one of chopped parsley.