If making the pastry by hand, combine the flour and salt in a large bowl. Use a pastry cutter to cut the cold butter into the flour or pinch the butter in the flour with your fingers until it has the consistency of coarse meal. Add the lemon juice and 6 tablespoons of water, drizzling it as evenly over the flour as possible. Fold the dough together with your hands until you are able to collect it into a dough ball, adding more water as needed.

If making the pastry in a food processor: Freeze the butter cubes for 15 minutes before starting. Blend the flour and salt together in the food processor bowl. Add the chilled butter cubes and pulse with the flour until the butter chunks are the size of peas. Drizzle the lemon juice and 6 tablespoons of water over the flour as evenly as you can and pulse the mixture together, adding more water as needed to get the dough to a stage where you can squeeze it together.

Shape the dough into a disk and wrap with plastic wrap. Refrigerate for at least 30 minutes.

Roll the crust out to fit a 9-inch deep-dish pie plate (about 13 inches). Transfer the pastry to the pie plate and pinch the edges into a decorative pattern. If using store-bought pie doughs, make a double crust. Unroll the first dough on the counter and brush ½ teaspoon of water over the top. Place the second dough on top of the first and roll the two out together to a 13-inch circle with a rolling pin. Transfer the double crust into the pie plate and pinch the edges into a decorative pattern. Chill the pie crust in the freezer for at least 20 minutes.

Place a baking sheet, pizza stone or pizza steel on the bottom rack of the oven, remove the remaining racks from the oven and pre-heat the oven to 375°F.

Whisk together the eggs, half-and-half and salt for a few minutes until well combined. Season with freshly ground black pepper.

Remove the chilled pie shell from the freezer. Place the spinach in the pie shell. Sprinkle the Gruyère cheese over top, followed by the cherry tomatoes. Break up the goat cheese and scatter the crumbles into the pie shell. Brush the edge of the pastry with a little bit of the egg mixture and pour the rest of it into the pie shell.

Transfer the quiche to the oven and bake at 375°F for 60 minutes, until it has set in the middle. If the crust gets too dark during the baking process, gently cover the quiche with aluminum foil or wrap a ring of aluminum foil around the pastry edge.

Let the quiche rest for 20 minutes before serving. Cut into wedges and serve warm with a side salad.