Remove the butter from the refrigerator and let it sit at room temperature for 30–45 minutes until very soft.

Wash, dry, and finely mince the parsley and chives until almost paste-like.

Peel and mince the garlic cloves as finely as possible or press them through a garlic press.

Zest the lemon with a microplane, then cut it and squeeze out 1 tablespoon of fresh juice, discarding any seeds.

Place the softened butter in a medium mixing bowl. Add the Dijon mustard, lemon zest, lemon juice, smoked paprika, cayenne pepper, kosher salt, and black pepper.

Add the minced parsley, chives, garlic, and horseradish (if using) to the bowl.

Using a fork or rubber spatula, mash and stir until the mixture is completely homogeneous with no streaks of plain butter remaining.

Transfer the butter onto a sheet of plastic wrap or parchment paper and roll it into a tight log about 1.5 inches in diameter, twisting the ends to seal.

Refrigerate the butter log for at least 1 hour, or until firm enough to slice cleanly.

Unwrap, slice into 1/2-inch rounds, and place a round on hot steak, chicken, seafood, vegetables, or bread just before serving so it melts into a glossy sauce.