Place your skillet over medium-high heat. Add the butter and let it melt completely. Wait until the butter starts to foam slightly.

Add the sliced mushrooms to the hot skillet. Spread them out into a single even layer. Do not crowd the pan during this step.

Let the mushrooms brown for five minutes. Do not stir them too often at first. This helps them get a nice dark color.

Stir in the minced garlic and fresh thyme. Cook these for just one minute. You will smell the amazing aroma right away.

Pour the veal stock into the hot pan slowly. Use your spoon to scrape the brown bits. These bits hold a lot of great flavor.

Lower the heat to a gentle simmer. Let the liquid reduce by half the volume. The sauce should look glossy and thick.

Season the dish with salt and black pepper. Give it one final stir before serving. Serve the mushrooms while they are still hot.