Begin by heating the extra virgin olive oil in a medium saucepan over medium heat. Once hot, toss in the finely diced onion. Cook for about 3-4 minutes until the onion is translucent. This foundational step provides the sweetness that builds the sauce.

Next, add the chopped garlic and the sliced mushrooms to the pan. Cook for another 5-7 minutes. Stir occasionally until the mushrooms are nicely browned. The aroma that wafts through the kitchen at this point? Pure magic.

Once your mushrooms are perfectly browned, sprinkle the all-purpose flour over the mixture. Stir well to combine. This step will help thicken the sauce as it cooks. Cook the mixture for an additional 1-2 minutes, allowing the flour to lose its raw taste.

Now for the fun part! Slowly pour in the Marsala wine, making sure to scrape up any lovely browned bits stuck to the bottom of the pan. These bits are packed with flavor. Let the wine simmer for about 3-4 minutes until it reduces slightly.

With the wine nicely reduced, it's time to add the rich beef stock. Stir well. Bring everything to a gentle boil and then reduce to a simmer. Let it cook for another 10-15 minutes, which allows the flavors to meld together beautifully.

Finally, season the sauce with salt and freshly ground black pepper to taste. If you're feeling fancy, add the thyme leaves and heavy cream at this stage for a richer finish. Your Carrabba's Marsala sauce is now ready to serve!