1Drizzle some oil into a medium skillet set over medium heat; sauté the onion for a few minutes, until soft. Add the garlic and kale and 1/4 cup water and cook for 4-5 minutes, until any excess moisture has cooked off. Transfer to a bowl and cool slightly. Stir in the feta, egg, salt and pepper.
2Preheat the oven to 375°F.
3Take two sheets of phyllo and stack them on a clean work surface; cover the rest with a tea towel so it doesn’t dry out. Fold back half of the top sheet, brush the sheet underneath lightly with butter, then fold the top sheet back down. Repeat on the other side.
4Cut the sheet in half lengthwise and then again lengthwise into quarters so you have 4 long strips. Place a spoonful of filling at one end of each strip and fold the corner over it diagonally, creating a triangle. Continue folding the strip (as if you were folding a flag), maintaining the triangle shape.
5Repeat with the remaining phyllo and filling, placing the packets seam side down on a baking sheet. (They can be prepared up to this point and frozen in a single layer on a baking sheet.) Brush the tops of the triangles with butter or oil and bake for about 20 minutes, or until golden.
6Makes 2 1/2 dozen triangles.