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Ingredients
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Parsley Sauce
Method
Parsley Sauce
Make a roux
Melt the unsalted butter in a medium saucepan over medium heat. Once foaming subsides but the butter is still bubbling gently, add the plain flour. Stir continuously with a whisk or wooden spoon to form a smooth paste (roux). Cook the roux for 1.5–2 minutes without browning to remove the raw flour taste.
Add liquids gradually
Reduce the heat to medium-low. Gradually add about half of the milk (about 1 cup) in a slow, steady stream while whisking vigorously to prevent lumps. When incorporated and smooth, pour in the vegetable stock while continuing to whisk. Finally add the remaining milk. Bring the mixture to a gentle simmer, whisking occasionally, until it thickens to a creamy sauce that coats the back of a spoon, about 4–6 minutes.
Season and finish
Stir in the finely chopped fresh parsley, English mustard (if using), sugar, sea salt, and freshly ground black pepper. Simmer gently for another 1–2 minutes to blend flavors and soften the parsley slightly. Taste and adjust seasoning: add lemon juice to brighten, more salt or pepper as needed. If the sauce is thicker than desired, whisk in cold water, 1 tablespoon at a time, until you reach a sauceable consistency (typically 1–2 tbsp).
Rest and serve
Remove from heat. Allow the sauce to sit for 2–3 minutes to let flavors meld; it will thicken slightly as it cools. Serve warm over boiled potatoes, steamed vegetables, fish, or as an accompaniment to cold meats. Reheat gently over low heat, adding a splash of milk if needed to loosen.