**Important: thaw puff pastry according to package directions**
Pre-heat the oven to 425F and line a baking sheet with parchment paper.
Role out the puff pastry dough into a 10 inch by 12 inch rectangle (approximately). Make a half-inch border around the tart by rolling/pinching the sides of the dough. Using a fork, make dots throughout the middle of the tart and then set aside.
To make the mushrooms, melt 2 tbsp butter in a frying pan over medium heat.
Once the butter is bubbling, add in the garlic and give it a quick stir. Then add in the sliced mushrooms. Cook the mushrooms for 5 minutes, stirring occasionally.
Add in thyme sprigs, salt and pepper to the mushrooms and cook for another 5 minutes, stirring often and until the mushrooms are softened. Remove the thyme sprigs and then set mushrooms aside.
Spread 1 cup of cheese onto the tart and bake for 10 minutes. Then remove from the oven. (Note: the middle of the tart may start to puff up a bit so when removing the tart after 10 minutes, just use a fork to make a couple more dots in the tart to get the air out)
Spread the mushrooms out evenly onto the baked cheese layer of the tart, then layer 1/2 cup remaining cheese on top of the mushrooms. Bake the tart for 12-15 more minutes until the crust is golden.
Top with arugula and enjoy!