Melt the butter in a small saucepan over medium heat. Add the minced garlic and saute for 1 minute, stirring constantly, until fragrant. Do not let the garlic brown or it will make the sauce bitter.

Add the flour and whisk continuously for about 2 minutes until the mixture is lightly golden and smells slightly nutty. This is your roux and it is what gives the sauce its body.

Gradually pour in the whole milk, whisking constantly as you add it to prevent lumps. Keep whisking and cook for 5 to 7 minutes until the sauce is thick enough to coat the back of a spoon.

Remove from heat and stir in the boursin cheese, freshly grated parmesan, salt, and black pepper until completely smooth and melted. The sauce should be creamy, garlicky, and thick enough to spread without running. Set aside.

Heat the olive oil in a skillet over medium high heat. Add the sliced cremini mushrooms in a single layer. Do not stir immediately. Let them sit undisturbed for 2 to 3 minutes so they develop a golden sear rather than steaming. Add the minced garlic, salt, and black pepper, then stir and cook for another 2 minutes until the mushrooms are golden, caramelized, and any liquid they released has evaporated. Set aside.

Preheat your oven to 425F and line a large baking sheet with parchment paper. On a lightly floured surface, gently roll out the thawed puff pastry sheet to smooth out any creases.

Transfer to the prepared baking sheet. Using a sharp knife, score a 1 inch border around the edges without cutting all the way through. This border will puff up into the crust during baking. Poke the inside of the border all over with a fork to prevent it from puffing too much.

Brush the scored border generously with the beaten egg wash. This gives you that deep golden color on the crust. Bake at 425F for 10 minutes until the border is puffed and starting to turn golden. Remove from the oven and press the center down gently with the back of a spoon if it has puffed up.

Spread about ¼ cup of the white sauce evenly inside the scored border using the back of a spoon. Keep the layer thin. Too much sauce will make the center soggy and bubble over the crust.

Sprinkle the mozzarella and fontina evenly over the sauce. Distribute the sauteed mushrooms evenly over the cheese layer.

Return to the oven and bake for 6 to 8 minutes until the cheese is fully melted, bubbly, and starting to turn golden at the edges. Watch it closely during this final bake.

Remove from the oven and immediately top with fresh arugula. Tear the burrata into pieces and scatter over the top. Drizzle with truffle oil and balsamic glaze and finish with fresh basil leaves. The residual heat from the pizza will soften the burrata slightly into the cheese layer. Serve immediately while the pastry is still hot and crispy.