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1
Preheat the oven to 400F (200C).
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2
Toss the sliced onions, 1 tablespoon of oil, salt and black pepper on a large baking sheet until well coated.
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3
Spread the onion slices evenly and roast for about 25 minutes until the edges of the onions start to become brown, stirring once after 15 minutes.
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4
Set aside.
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5
Add the remaining oil in a large skillet over medium-high heat until hot.
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6
Cook the garlic for about 40 seconds until very fragrant.
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7
Add the mushrooms and the stems of swiss chard, stirring often, and cook until the mushrooms are soft and the stems are tender 3 to 5 minutes.
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8
Add the swiss chard leaves, and cook for 2 to 3 minutes until the leaves are wilted.
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9
Season with salt and black pepper to taste.
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10
In a large bowl, with a rubber spatula mix together bread, ricotta cheese, feta cheese, cooked mushroom - swiss chard mixture, and roasted onions until well combined.
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11
Place the mixture evenly into a 8 to 10-inch oven proof cast iron pan or nonstick skillet.
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12
Whisk together the eggs and milk in the same mixing bowl until well blended.
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13
Pour the liquid mixture over the filling in the pan.
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14
Bake in 400F (200C) for 20 minutes, lower the oven temperature to 350F (180C) F and bake for another 25 minutes or longer until the frittata is set and the top starts to brown.
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15
At the last 1 or 2 minutes, turn on the broiler to brown the top more if needed.
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16
Cool for about 10 minutes, cut into wedges and serve warm.
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17
The handle of the pan will be hot for a while, make sure to use oven mitt or kitchen towel to cover it every time before you touch the handle.
