Pre-heat the oven to 425 degrees F. Line a baking sheet with parchment paper and set aside.

Melt butter in a skillet. Add in the mushrooms. Cook, stirring frequently, until they are softened and reduced in size. Season with salt and set aside to cool.

To make the asparagus topping: Gently mix asparagus, scallions, garlic, salt, and pepper in a bowl.

Reserve 1 tablespoon of the goat cheese and set aside.

Mix the rest of the goat cheese and olive oil in a bowl.

To assemble the tart: Carefully unfold the puff pastry on a lightly floured surface. Using a roller, roll it into a 10x10 square dough. Transfer it onto the parchment lined sheet.

Spread goat cheese-oil mixture over the puff pastry leaving a 1-inch border throughout the sides. Top it with mushrooms and asparagus mixture making sure that they are evenly distributed throughout the tart.

Brush sides with a little bit of water and fold it onto itself, towards the middle, on all sides.

Bake in the oven for 15 minutes or until the sides of the tart turn golden brown.

Let it cool for 5 minutes. Scatter the reserved goat cheese in small chunks all over the tart.

If using, garnish with arugula and prosciutto.

Slice it into smaller pieces and serve while it is still warm.