1/2 cup warm milk
1/4 cup plus 1 Tbsp warm water
1 3/4 tsp active yeast
2 cups flour (you can swap out half whole wheat flour--just add an additional Tbsp water)
3/4 tsp salt
1 Tbsp olive oil
1 bunch Russian or lacinato kale, washed and finely chopped
1 small bunch flat-leaf parsley, washed and finely chopped
3/4 cup feta
2-3 Tbsp melted butter or olive oil
1 egg, beaten
1 Tbsp sesame seeds
To make the dough: Pour the water and milk in a mixing bowl, sprinkle on the yeast, and allow to soften for a few minutes. Add the flour and salt, kneading with your hands or a dough hook for several minutes until you create a soft, pliable dough that just clears the sides of the bowl (if it doesn't, add a touch more flour). Cover and let sit for a few minutes while you prepare the filling.
To make the filling: Heat the oil over medium heat in a large pot. Add the kale and stir to coat with the oil, and sprinkle with a very light dusting of salt to draw water out. Cover and cook, stirring occasionally, until the kale is softened. Add the parsley, and cook an additional minute. Remove from heat and stir in the crumbled feta.
To assemble and bake: Divide the dough into 3 equal pieces. Roll out the first piece to form a large rectangle, ~15"x17". Drizzle it with the melted butter or olive oil, and then scatter half the filling evenly over the top. Roll out the second piece of dough, lay it on top of the first, and repeat the process with melted butter and the remaining filling. Roll out the final piece of dough, lay it over the top, and drizzle with the remaining butter.
Fold the right- and left-hand sides in, so that they meet in the middle (you can consult the pictorial on this page, which gives you a better idea of the whole process). Repeat with the top and bottom, so you have a nicely folded package. Flip it upside-down, so the smooth underside is on top. Roll it gently with a rolling pin, taking care to not tear the dough while you ease it into a roughly 8" square. If you have parchment paper, place the borek on a large square of it. With a large knife, cut through all the layers halfway through each side and on the diagonal, yielding 8 little triangles. Pick up the parchment, and transfer the cut square into an 8" brownie pan (if you don't have parchment, just make sure your pan is well-greased). Cover lightly with a clean dishtowel, and let rise for about 1 hour.
When the dough is almost done rising, preheat your oven to 375 degrees. Gently brush the dough with the beaten egg, and sprinkle with sesame seeds. Place in the oven and bake until lightly browned, ~30-45 minutes. Let cool and serve.