1. Be sure to take out a pan and get ready to saute. In a saute pan turn it on to a medium heat. Once the pan is warm, be sure to add olive oil. Once this is done go ahead and add the mushrooms, shallot, thyme, salt and pepper. Let all the ingredients you added to saute for 5 minutes. Once the 5 minutes have passed, you can go ahead and add the cognac. Allow the cognac to cook for 1 minute until the alcohol is absorbed. After allowing the alcohol to be absorbed, remove the mushroom mixture from the pan and place in a large bowl.
2. Take out a separate pot for this next step. In this separate pot, start by adding milk and heat. Allow the milk to reach just a boil. We don't want to have the milk boiling completely, we just want to make sure that the milk is hot.
3. If you have a 4 quart pot, you're going to need it for this step. In a 4 quart pot start by putting it on low heat. Once the pot is getting warm, start by adding truffle butter. Allow the truffle butter to melt. Once you can see it melting, slowly start whisking in the flour. You are going to want to keep whisking everything for 2 minutes or until the flour taste is cooked out. This is important, if it's not ready keep whisking!
4. Once everything looks good, start by slowly adding the hot milk to the butter flour mixture. Remember, be sure to be constantly whisking until all the milk has been added. Once all the milk has been added, let it cook on a low for about 2 minutes. Allowing it to cook will let the bechamel sauce thicken up. Don't forget though, constantly keep whisking the sauce. Then you can go ahead and add the nutmeg, salt and pepper to the bechamel sauce.
5. Now it's time to turn the bechamel sauce off. Once you turned the sauce off, you need to immediately combine all the grated cheeses to the bechamel sauce. Be sure to stir the sauce and all the cheeses. Stirring the sauce will allow everything to melt into one thick cheesy sauce.
6. By this time, the pasta should be ready and cooked at the same time your bechamel sauce is done. This makes everything much easier for you in the kitchen. Make sure to under cook your pasta by 1 minute because it will cook further in the oven. If you don't under cook the pasta, the pasta will end up being really soggy and we don't want that.
7. This is the fun part! Go ahead and grab one large bowl. In the large bowl you're going to start combining some more of the yummy ingredients. Start by combining the mushrooms, pasta and bechamel sauce. Stir to incorporate all of the ingredients.
8. Okay, you're almost done! Grab a nonstick pan. Place olive oil and garlic into the nonstick pan. Bring the pan to a medium heat. Once the pan is warm go ahead and cook the garlic for 1 minute. Once the minute is up, go ahead and add the panko, salt and pepper. Cook these ingredients for 2 minutes until it is slightly browned.
9. It's almost time to start eating! Add the mac & cheese to your favorite baking pan top with the crunchy browned panko. Go ahead and let it bake on 375 degrees for 30 minutes until the cheese is bubbling and the panko is browned. Then just go ahead and let the mac and cheese cool off. Once your dish is cooled, you can go ahead and dig right in! It will be so cheesy and delicious!