Preheat oven to 400 degrees F.
Make your pie crust according to the directions in the post. Roll out into a large thin circle that is larger than your tart pan so that when you transfer it to your pan, it will cover the bottom and go up the sides.
Gently fold dough into quarters, transfer to tart pan, unfold, and press dough up the sides. Use the rolling pin to roll over the top and cut off any excess dough. Use your fingers to push up the sides to raise the dough up a little taller than the edge all around.
Directly cover the dough with aluminum foil and weigh down with pie weights, dry rice, or uncooked beans. Bake in the preheated oven 8-9 minutes covered and then another 2-3 minutes uncovered. Remove from oven just when dough is starting to turn golden.
While the crust is cooking, prepare the filling. Over medium high heat, melt butter in large saute pan and add the onion and mushrooms. Stir occasionally and allow to cook until golden brown, about 10min. Add spinach and garlic. Continue cooking until all of the liquid has evaporated, about another 5-10 minutes. Add wine and scrape the bottom of the pan with a wooden spoon to release any goodness and deglaze pan. Allow to cook until all liquid has evaporated, about another 5 minutes.
Reduce oven temperature to 375 degrees F.
In large bowl, whisk together eggs, cream, and milk. Stir in sauteed veggies and half of the shredded cheese. Gently pour into pastry shell - it will go all the way to the top. Sprinkle top of quiche with remaining cheese.
Bake in preheated oven until slightly puffed and golden brown, about 25-30 minutes. Remove from tart pan to cut.
Serve warm with baby spinach that has been lightly dressed in olive oil and lemon juice.