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1
Preheat oven to 350 degrees.
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2
Heat oil over medium heat in a large, heavy skillet and add onion.
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3
Cook, stirring, until tender, about 5 minutes, and add a generous pinch of salt, the garlic, peppers and thyme.
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4
Cook, stirring often, for 5 minutes, then turn the heat to medium low and continue to cook for 5 to 10 minutes more, until peppers are very tender and sweet.
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5
Turn up heat to medium-high and, a handful at a time, add spinach and stir until each handful wilts.
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6
If there is liquid remaining in the pan turn up the heat and stir while you let it cook off.
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7
Remove from heat and transfer to a bowl.
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8
If you are making filling a day ahead, refrigerate uncovered.
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9
Beat together egg yolks and eggs in a medium bowl.
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10
Set tart pan on a baking sheet for easy handling.
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11
Using a pastry brush, lightly brush bottom of the crust with some of the beaten egg and place in oven for 5 minutes.
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12
Add salt (I use 1/2 teaspoon), pepper, and milk to the remaining eggs and whisk together.
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13
Spread pepper and spinach mixture in an even layer in the crust.
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14
Stir together cheeses and sprinkle in an even layer on top.
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15
Very slowly pour in the egg custard over the filling.
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16
If your tart pan has low edges, you may not need all of it to fill the shell, and you want to avoid the custard spilling over.
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17
Place quiche, on baking sheet, in the oven and bake for 30 to 35 minutes, until set and just beginning to color on the top.
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18
Remove from oven and allow to sit for at least 10 minutes before serving.
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19
Serve hot, warm or room temperature.
