Preheat oven to 425 degrees Fahrenheit (220 degrees Celsius).

Peel the sweet potatoes and, using a very sharp knife, cut into one eighth of an inch (.3-cm) rounds. Spray a round baking dish or tart pan with cooking spray and lay some of the sweet potatoes on the bottom of the pan, overlapping somewhat so there are no gaps. The sweet potatoes will shrink while cooking, so make sure the slices overlap enough. Take additional slices and stand them up around the edge of the pan, overlapping by about quarter inch (.6-cm), creating a crust. Spray again and season with 1/2 teaspoon salt and a pinch of pepper.

Bake for 25 minutes or until the top edges are starting to brown. Remove from oven and let cool. Lower oven heat to 350 degrees Fahrenheit (180 degrees Celsius).

Meanwhile, heat olive oil in a large frying pan and sauté the onions and garlic until they’re lightly golden. Remove from heat and add the eggs, remaining teaspoon of salt, and 1/2 cup panko crumbs. Pour into prepared crust and sprinkle with the remaining panko. Bake for one hour or until set.