Brown Butter Sauce

Instructions

1. Prepare the butter
   Cut the cold unsalted butter into small, even-sized cubes to ensure it melts evenly. If using hazelnuts, toast them lightly in a dry pan until fragrant, then chop finely and set aside.
2. Brown the butter
   Place the butter in a light-colored saucepan over medium heat. As the butter melts, it will begin to foam. Swirl the pan occasionally to ensure even cooking. Watch carefully as the color changes from yellow to golden to a nutty brown, about 5-7 minutes. You'll notice brown specks forming at the bottom - these are the milk solids caramelizing.
3. Monitor the color change
   Remove from heat immediately when the butter reaches a hazelnut-brown color and gives off a nutty aroma. Transfer to a bowl to stop the cooking process if not using immediately, as the butter can quickly go from brown to burnt in the hot pan.
4. Add aromatics
   Return the brown butter to low heat (if transferred to a bowl) and add the minced shallot. Cook for 1 minute until softened but not browned. Add the lemon juice (it will sizzle), capers if using, salt, and pepper.
5. Finish the sauce
   Remove from heat and stir in the chopped parsley and toasted hazelnuts if using. The sauce should be served immediately while warm, as it will solidify when cool. If needed, it can be reheated very gently.