Preheat your oven to 350°F / 175°C.
Arrange the kale leaves in a single layer on two baking sheets and lightly coat with cooking spray.
Bake until the leaves are soft but not yet crisp, about 10 minutes.
Remove from the oven and set aside. 2. Increase the oven temperature to 400°F / 200°C. On one of the baking sheets, combine the diced sweet potato and sliced leeks.
Drizzle with olive oil, season with a pinch of salt and pepper, and toss to coat.
Spread in a single layer. 3.
Roast the vegetables for 15 to 20 minutes, stirring once, until they are golden brown and tender. 4.
While the vegetables roast, whisk together the whole eggs, egg whites, milk, pesto, and another pinch of salt and pepper in a large bowl. 5.
Line a 12-cup muffin pan with the baked kale leaves, creating a cup-like liner. Allow the tops of the leaves to stick out about 2 inches above the rim. 6.
Divide the roasted sweet potato and leek mixture evenly among the 12 kale-lined cups. 7. Carefully pour the egg mixture into each cup, filling them almost to the top.
Place the muffin pan on a baking sheet to catch any potential spills. 8.
Bake for about 30 minutes, or until the quiches are puffed, set, and cooked through. 9.
Let the quiches cool in the pan for a few minutes. To remove, run a small knife around the edges to loosen, then gently lift them out.
Serve warm or at room temperature.
