Bring the chicken stock to the boil in a large pan.
In a heavy-based saucepan, melt 100g of the butter. Add the onions and sweat gently until translucent. Add the garlic, parsnips, and potato, and stir to coat.
Pour in the hot chicken stock. Bring back to the boil, then reduce to a simmer and cook for 18 minutes, or until the vegetables are soft.
Add the double cream and simmer for a further 3 minutes.
Stir in the truffle honey.
Remove from the heat and blend until completely smooth.
Pass through a fine sieve for a refined texture.
In a separate pan, melt the remaining 150g butter and cook over a high heat, whisking continuously until it turns a light brown hazelnut colour.
Whisk the brown butter into the soup.
Season with salt, pepper, and lemon juice to finish.
