Position the oven rack in the lower third of the oven and preheat to 350º F (180 º C).

On a lightly floured surface, roll pie dough into a 12-inch circle. Line a 10-inch quiche dish or pie plate with the dough, pressing into the bottom and up the sides. Tuck the excess dough around the edges under and crimp as desired. If using store-bought, simply unroll the pie crust and press into a 9" quiche dish or pie plate, crimping the top edges if desired. Chill the pie crust in the refrigerator for at least 30 minutes and up to 5 days.

Extra step for extra crispy crust: Line the chilled pie crust (in the quiche dish) with parchment paper. Fill with pie weights or dried beans. Make sure the weights are evenly distributed around the pie dish. Bake until the edges of the crust start to brown, for about 15 minutes. Remove the pie from the oven and carefully lift the parchment paper (with the weights) out of the pie. Prick the bottom and sides with a fork (about an inch apart). Return the pie crust to the oven. Bake until the bottom crust is just beginning to brown, about 8 minutes. Remove from the oven and set aside. Note: You can skip this step if you don't care for a crispy crust bottom.

Place butter in a large skillet over medium heat, when melted add chopped shallots, spread them out in an even layer to ensure they cook evenly. Let the shallots cook, stirring occasionally, until they become soft and translucent, about 3 minutes. Add the fresh baby spinach, they may seem bulky at first, but they'll quickly wilt down as they cook. Using tongs or a spatula, gently toss the spinach in the skillet to coat it with the butter and shallots. Cook the spinach, stirring occasionally, until it wilts down and reduces in volume, about 3 minutes. Set aside.

Mix the ricotta, cornstarch, heavy cream, garlic powder, onion powder, salt, black pepper, ground mustard, nutmeg, and baking powder in a bowl. Then, add the sautéed shallots and spinach mixture and half of the crumbled feta cheese; mix to incorporate.

Spread the mixture over the pie crust and use a spatula to even the top. Sprinkle the remaining ½ cup of feta cheese on top.

Bake for 40 - 45 minutes or until set and golden brown on top. Let cool for 15 minutes before slicing and serving.