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1
Preheat the oven to 450 degrees F. Grease a 9-by-13-inch baking dish with oil.
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2
Fill the bottom of the dish with one layer of the potatoes (about 4 cups).
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3
Drizzle the potatoes with 1 tablespoon of the oil.
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4
Bake until hot and crisp, about 20 minutes.
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5
Let cool for 15 minutes.
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6
Meanwhile, heat the remaining 2 tablespoons oil in a large skillet over medium-high heat.
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7
Add the onions and red and green peppers.
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8
Season with 1/2 teaspoon salt and a few grinds of black pepper.
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9
Cook, stirring occasionally, until the vegetables have softened and started to brown, about 6 minutes.
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10
Add the corned beef, and cook for 2 minutes more.
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11
Let cool.
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12
Whisk together the eggs, milk, mustard, hot sauce, 1/2 teaspoon salt and 1/4 teaspoon ground black pepper in a large bowl.
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13
Sprinkle 1/2 cup of the Cheddar over the potatoes in the casserole dish.
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14
Layer the vegetable-beef mixture over the Cheddar.
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15
Top with the remaining cup of Cheddar.
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16
Pour the egg mixture into the dish.
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17
(The casserole can be assembled up to this point and refrigerated overnight.
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18
Remove from the refrigerator 30 minutes before baking.)
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19
Preheat the oven to 350 degrees F. Top the casserole with the remaining potatoes (about 2 cups).
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20
Bake until the egg mixture is set and the top is lightly golden brown, 50 to 60 minutes.
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21
Let cool for 15 minutes before serving warm or at room temperature.