Peel the sweet potato and cut into thin 1/8-inch slices. If possible, use a mandoline for uniform slices. 

Arrange part of the sweet potato slices in the prepared dish to cover the bottom. Cut enough of the remaining slices in half to line the edges of the dish. Sprinkle the rounds with salt and freshly ground black pepper. 

Transfer the dish to the oven and bake for 10-minutes. Remove and set aside to cool slightly.

Meanwhile, add the kale to a large plate, drape a paper towel over the kale and microwave for 1-2 minutes until lightly wilted. Remove from the microwave, discard the paper towel and let cool. With kitchen scissors, cut the kale slightly. Set aside

Add the olive oil to a skillet set over medium-high heat and when it is hot add the leek and bell pepper slices, cook until just beginning to soften. Remove the skillet from the heat.

Arrange the leek and red bell pepper slices over the dish of cooled sweet potatoes. 

Distribute the kale over the veggies.

Add the soft goat cheese to a mixing bowl with the sour cream and using an electric mixer beat until well combined. Add the eggs and continue mixing to a smooth and creamy consistency. Stir in the thyme leaves, salt pepper and red pepper flakes.

Pour half of the egg mixture into the dish over the vegetables. 

With a fork, lift the mixture slightly to allow the egg mixture to settle around the veggies, then add the remaining egg mixture. Add additional cut strips of sweet potato, sliding them down into the egg mixture.  

Place the dish into a rimmed baking sheet and transfer to the oven. Bake for 45-50 minutes until golden, puffed and the center is set. Remove from the oven and allow to cool 5 or 10 minutes before serving.