Place the oven rack in the lower-middle position and preheat the oven to 375 degrees farenheit.
With a fork, prick the bottom of the crust at ¼ inch intervals.
Place the prepared, chilled crust on a rimmed baking sheet and line with foil before filling completely with pie weights. Press the weights firmly into the corners of the crust and press the overhang of dough against the outside of the cake pan to ensure there is no slumping!
Bake for 30-35 minutes, until lightly golden brown around edges.
Remove pie weights and foil or parchment and bake crust for another 15 minutes, until bottom is golden brown.
Remove crust from oven and brush interior with reserved egg white and reduce oven temperature to 350 degrees farenheit.
While the crust is blind-baking, saute the shallots in the 2 T. of butter over medium-low heat until softened and slightly caramelized, 6-8 minutes. Add the blanched, chopped spinach and cook briefly, seasoning to taste with salt and pepper. Set aside to cool.
Whisk the 8 eggs plus the extra yolk in a large mixing bowl until foamy and well combined. Mix in the heavy cream.
Whisk a small portion of the milk (about 3 T) with the cornstarch until completely smooth. Pour the cornstarch/milk mixture and the remaining milk into the eggs and heavy cream.
Add the ½ t. salt, the ¼ t. pepper, along with the grated nutmeg. Gently stir in the cooled shallot/spinach mixture as well as the gruyere.
Pour the filling into the chilled, prepared pie crust. Gently push down the vegetables and cheese into the custard in an attempt to remove any air bubbles and disperse filling evenly.
Place the quiche back onto the rimmed baking sheet and bake at 350 for 1 and ¼ hours up to 1 and ½ hours, until the top is deeply browned and puffed, and the eggs are fully set.
Remove from the oven and cool on a cooling rack for 30-40 minutes.
Gently pull tabs of foil out of the cake pan to remove the quiche. Carefully, slip foil out from under crust and slice into 8 servings. A serrated knife works best. Enjoy!