Cut the monkfish into 2-3 cm cubes. Slice the chives finely.
Heat 2 tablespoons butter over medium-high heat in a large pan. Add the monkfish cubes and cook for 1-2 minutes.
Pour the white wine into the pan. Cover and cook for 2-3 minutes.
Remove the monkfish cubes from the pan and season with salt and pepper. Set aside to keep warm.
Pour the vermouth and fish stock into the pan. Bring to a simmer over medium heat and reduce for about 5 minutes until roughly half the liquid remains.
Stir in the cream and simmer for 2-3 minutes until the sauce thickens to a creamy consistency.
Remove from heat. Whisk in the cold butter pieces until the sauce is smooth and glossy. Season with salt and pepper to taste.
Return the monkfish cubes and chives to the sauce. Warm through over low heat for 1-2 minutes, stirring gently. Do not boil.