Boyus or Boyuz or Boyikus are spinach and cheese filled Sephardic pastry. I have tried many recipes and I think at least three are archived on this blog in the recipe index. Last week when I was researching and making strudel I had a thought. Strudel dough is essentially like philo dough. Nona says that her mother made her own philo dough for the boyus. You see where I am going with this. I made two batches of strudel dough and instead of butter for brushing the dough; I used olive oil for one trial and sunflower oil for the second trial.
I am happy to report that both versions were a stunning success. The boyus were flaky, crispy, light as a feather, and brimming with that good spinach, feta, parmesan, salty taste. My son was keeping me company at 1:00 AM when they came out of the oven. As soon as they were cool enough to not burn our mouths, we bit in, and the flaky crunch with cheesy spinach was the best. Jacob had seconds.
1 plastic container prewashed baby spinach
7 ounces Bulgarian Feta cheese, crumbled
4 ounces sharp cheddar cheese, grated or shredded
1/2 cup parmesan cheese grated (I prefer Parmesano Reggiano)
3 cups all purpose unbleached flour, plus ¼ quarter cup for kneading
1/ 2 teaspoon salt
1 cup warm water
4 tablespoons sunflower oil
1 teaspoon apple cider vinegar
Additional flour for dusting
¾ cup olive oil
½ cup finely grated Parmesan Cheese
To make filling, use a sharp knife to slice spinach into thin ribbons and then, chop spinach into small pieces. Place spinach in a large bowl. Add grated and crumbled cheese, toss to mix. Set aside or refrigerate while you make the dough.
Place flour and salt in the mixing bowl of a stand mixer. Add warm water with oil, and vinegar to flour. Beat until a ball of dough forms, about one minute. Let the dough rest for 10 minutes. Touch the dough to determine how sticky it is. Add remaining ¼ cup of flour and beat dough until soft, smooth, shiny, and easily removable from the mixer paddle. Place the smooth ball of dough in an oiled bowl and cover with a tea towel to rest for about one hour. This dough does not rise. During the resting time, prepare the stretching table. For the stretching, I recommend a kitchen table covered with a clean white bed sheet dusted in flour. I know the sheet is red in the picture, but it made it easier to shoot the picture. 
Pre heat oven to 375° F. Remove dough from the bowl where it has been resting. Place it in the center of the floured sheet on the table. Give the dough a couple of passes with a wood rolling pin to make a rectangle, and then start to stretch by hand. Before stretching, remove all jewelry. Next, close your hands into a fist, and with the knuckle side up, slide your hands under the dough. Use the tops of your hands and move them methodically around the perimeter to expand the dough. The dough will stretch easily. Carefully work your way around forming a rectangle. Then go deeper toward the center, ever expanding. Work slowly and methodically, don’t rush dough. Continue stretching until dough is about a 32 inch by 40 inch rectangle. Use a scissor to trim the thick edge that is left on the perimeter. Brush the dough lightly with olive oil using a pastry brush. I recommend a silicone brush to prevent any tearing.
 Place filling down the long side of one edge, about 3 inches in from the edge, in a narrow mounded up column. Grab the edge of the sheet with your hands, and start to roll up the cylinder. Brush the cylinder with more oil if needed while you roll, brushing any excess loose flour away at the same time. When you are finished rolling the Boyu, seal the two ends. Carefully lift one end of the Boyu onto a prepared baking sheet lined with a silpat or parchment paper and make an S shape on the pan with the rest.  Brush top with oil, sprinkle on remaining Parmesan, and place the pan in the oven to bake. Bake until golden brown and cooked through about 30 minutes. 
Cut in slices and serve hot and crisp. This should make about 8-12 servings. You may reheat Boyus the next day in a 350° F oven for 10 minutes. You will notice, in some pictures I made coils instead of a long single Boyu to serve in slices. To make coils, after I stretched out the dough, I divided it with a sharp knife into 8 rectangles. I filled and rolled the rectangles individually and coiled them after I sealed the edges.