Heat butter in a heavy saute pan or sauce pan over medium heat.

Add minced celery, onion, carrot, and leek to the pan.

Cook the vegetables slowly, stirring occasionally, until they are well browned.

Sprinkle flour over the browned vegetables and toss to coat.

Continue to cook, stirring constantly, until the flour is also lightly browned.

Stir in red wine, beef stock, concentrated brown stock, thyme, and bay leaf.

Press garlic into the mixture using a garlic press.

Partially cover the pot and bring the sauce to a simmer.

Reduce heat to low and simmer for about 1 hour, stirring occasionally.

Remove the lid and continue to simmer, allowing the sauce to thicken to the desired consistency.

Pass the sauce through a food mill to remove any solids and create a smooth texture.

Season the sauce to taste with fine sea salt and freshly ground pepper.