Step 2

Grease a 9-by-13-inch casserole dish with the room-temperature butter.

Step 3

In a large sauté pan, heat the oil over medium heat. Add the leeks to the pan and sauté until tender, 2 to 3 minutes. Add the kale in handfuls and cook until it wilts, 2 to 3 minutes more.

Step 4

In a large bowl, toss the vegetable mixture with the bread and goat cheese, and then transfer to the prepared casserole dish.

Step 5

In a large bowl, whisk the eggs with the milk, cream, mustard, salt and pepper to combine. Carefully pour the custard evenly over the bread mixture. Cover the dish with plastic wrap and refrigerate overnight.

Step 6

Preheat the oven to 375°F. Bake the strata until the custard is set and the surface is golden brown, 25 to 30 minutes.

Step 7

Serve warm or at room temperature.