1. Preheat the oven to 375°F. Put the butter in a large skillet, preferably nonstick, over medium heat. A minute later, add the 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 the heat, add the herbs, then taste and adjust the seasoning.
2. Meanwhile, hard-cook 3 of the eggs , then shell and coarsely chop. Add to the cooked kale mixture and let cool while you make the batter.
3. Combine the yogurt, mayonnaise, and remaining eggs. Add the baking powder and flour and mix until smooth. Lightly butter a 9 × 12-inch ceramic or glass baking dish. Spread half the batter over the bottom, then top with the kale filling; smear the remaining batter over the kale, using your fingers or a rubber spatula to make sure there are no gaps in what will form the pie’s top crust.
4. Bake for 45 minutes; it will be shiny and 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.
An Eastern European classic: Replace the kale with 1 medium head of Savoy or white cabbage and the mixed herbs with 2/3 cup snipped fresh dill.
Mushroom and Kasha Pie.
Meaty in flavor and texture and can be made with almost any cooked grain, including wheat and rye berries: Substitute 3 cups chopped or sliced mushrooms for the kale and add 1 cup cooked kasha . Add the kasha to the mushroom mixture along with the herbs.