Melt butter in a large skillet, preferably nonstick, over medium heat. Add kale and onion. Sprinkle with salt and pepper and cook, stirring occasionally until the leaves are quite tender, about 10 minutes. Do not brown. Remove from heat, add the herbs, then taste and adjust the seasoning.
Peel and coarsely chop the hard-boiled eggs. Add to the cooked kale mixture and let cool while you prepare the batter.
Combine yogurt, mayonnaise and remaining eggs in a large bowl. Whisk to mix well.
Add baking powder, salt and flour to the egg mixture and mix until smooth.
Lightly butter a 9×13-inch glass baking dish. Spread half of the batter over the bottom.
Top with kale filling. Smear the remaining batter over the kale, using a rubber spatula to make sure there are no gaps in what will form the pie’s top crust.
Bake for 45 minutes in a 375F preheated oven, until golden brown.
Let the pie cool for at least 15 minutes before slicing it into as many squares or rectangles as you like. Eat warm or at room temperature.
Sydney, Frances and Frank, thank you making this healthy pie.