To make the pastry, in a bowl, stir together the flour and salt. Add the butter and, using a pastry blender, cut it in until the mixture resembles coarse meal. In a small bowl, using a fork, beat the egg with 2 Tbs. of the ice water. Make a well in the flour mixture and pour in the egg mixture and 2 more Tbs. ice water. Using the fork, mix lightly, adding more ice water as needed until the mixture holds together. Pat into a ball, wrap in plastic wrap and refrigerate for 1 hour.
On a floured pastry board or other work surface, roll out the pastry into a round about 13 inches in diameter. Transfer to an 11-inch tart pan with a removable bottom, turn under the edges to make them flush with the pan rim, and prick the bottom in several places with a fork. Press a piece of aluminum foil, shiny side down, onto the crust, and freeze for about 30 minutes.
Preheat an oven to 425°F
Bake the foil-lined pastry shell for 8 minutes. Remove the foil and continue baking until the crust looks dull, about 4 minutes more. Remove from the oven, sprinkle with the Swiss cheese, and reduce the oven temperature to 375°F
Meanwhile, make the filling: Drain the spinach and squeeze dry. In a large sauté pan over medium heat, melt the butter with the olive oil. Add the yellow and green onions and garlic and sauté until soft, about 4 minutes. Add the spinach and sauté, stirring, until completely wilted, about 3 minutes. Add the dill and pepper and continue sautéing for about 2 minutes more. Taste and adjust the seasonings; the mixture should taste peppery. Let cool for 5 to 6 minutes.
In a pitcher or bowl, whisk the eggs until blended, then whisk in the half-and-half and cream. Crumble the feta cheese into the spinach and stir in the egg mixture. Pour into the prebaked shell.
Bake until the filling is puffed and light brown and a knife inserted into the center comes out clean, 35 to 40 minutes. Remove from the oven and let stand for 5 to 10 minutes. Garnish with the olives and serve.