Preheat the oven to 400°F. Then slice the mushrooms any way you like. Melt a knob of butter (about 2 tbsp) in a deep pan. Once the butter is melted, toss in the mushrooms and saute them till they turn soft.
Season with salt and pepper and turn up the heat, you want to keep the filling as dry as possible. Then toss the heaping pile of baby spinach and watch it reduce to less than half.
Once the spinach is wilted and most of the water in the pan dried out, add the dijon mustard and stir well to coat all the mushroom and spinach. Then turn the stove off.
Once your oven is preheated, roll out your pie crust and press it into a well greased loose bottom quiche pan or pie dish. Cut the excess off. Using a fork, poke holes in the bottom of the crust.
Now you need to blind bake the crust. That means filling up the crust with baking beads or any kind of beans to prevent it from puffing up and baking it till it’s a light golden.
After around 10 minutes you can take out the beans and bake the crust for another 5 minutes so the bottom turns a light golden.
While the crust is baking you can prep the other filling. Cut up or crumble the goat cheese. And in a bowl, whisk together 2 eggs and 3/4 cup of heavy whipping cream and season it with salt.
To assemble the quiche, start by placing half the goat cheese in the bottom of the crust and then spread the spinach and mushroom filling evenly over it. Pour in the egg and cream mix and top with the remaining goat cheese.
Bake at 400°F for 20 minutes and then turn on the broiler for 5-7 minutes till it’s a nice golden on top.