How to Make It
In a large bowl, whisk the flour with the salt. Using a pastry blender, cut in the butter until the mixture resembles coarse meal. Lightly beat the egg with the water and sprinkle over the flour mixture. Stir with a fork to lightly blend, then squeeze gently until a dough forms. Pat into a disk, wrap in plastic and refrigerate for at least 30 minutes.
Preheat the oven to 350°. On a lightly floured surface, roll out the pastry to a 14-inch round about 1/8 inch thick. Fit the round into a 12-inch tart pan with a removable bottom and trim the overhang. Refrigerate the shell for at least 20 minutes.
Line the tart shell with foil and fill with pie weights or rice. Bake until the pastry is firm, about 30 minutes. Remove the foil and weights and bake for about 10 minutes longer, or until golden brown. Transfer the shell to a rack to cool.
Heat a large skillet. Add a large handful of the spinach and cook over moderately high heat, stirring, until wilted. Transfer to a colander set over a bowl. Repeat until all of the spinach has been cooked; let cool. Squeeze the spinach dry and coarsely chop it. Toss the spinach with the garlic and spread it in the cooled pastry shell.
In a medium bowl, whisk the milk with the cream, eggs, egg yolks, salt and pepper. Arrange the goat cheese rounds on the spinach. Pour the custard into the shell and bake for about 40 minutes, or until just set. Transfer the quiche to a rack to cool slightly. Cut into wedges and serve.