Step 1

Preheat oven to 350 F.

Step 2

Heat a large skillet over medium heat and add the olive oil. Once the oil easily moves around the pan, add the butter and let it melt.

Step 3

Add the sliced onions to the skillet and let them cook, stirring occasionally until they're caramelized (about 10 minutes).

Step 4

Stir in the spinach, and saute until it's wilted and the moisture has evaporated (about 5 minutes). Remove the pan from the heat.

Step 5

In a large bowl, whisk together the eggs, whole milk, and salt and pepper, to taste.

Step 6

Add the spinach mixture to a greased, 9-inch pie plate or quiche dish. Top with the cheeses before pouring in the egg mixture.

Step 7

Place the pan in the oven and bake for 30-35 minutes, until the eggs are set and the top is golden brown.

Step 8

Let the quiche cool for 5 minutes, then slice into 8 pieces and enjoy.