Start by making the dough. Prepare the yeast in a large mixing bowl for a stand mixer by whisking it with warm water and 1 teaspoon sugar. Let yeast stand until it foams and puffs up, about 10 minutes. If it doesn’t get foamy, your yeast is bad or the water was too warm or cool. Try again!
Using the whisk attachment for the stand mixer, mix in the remaining sugar, 1 egg and 3 egg yolks, oil and honey into the yeast mixture. (You can just use a whisk if you’re doing this by hand too) Then gradually add 3 cups flour and salt and either with a hook attachment using a stand mixer or a spoon and your hands until combined. Knead for about 10 minutes adding flour as needed, and form into a ball. Dough should be soft, smooth and slightly tacky.
Place the dough in a bowl greased with oil and cover. Let dough ferment in a warm place until it has doubled in size, about 2-3 hours. I put mine on top of an oven heated to 200 degrees.
Meanwhile, make the filling. In a large sautepan, cheat butter over medium heat and then add garlic and salt. Lower heat to medium-low and saute for a minute until garlic starts to brown and is fragrant. Then add the spinach and stir just until wilted. Cool the spinach while draining in a colender so it gets very dry. Lightly even more with towels.
Place the cooled, dry, spinach mixture in a bowl and add parmasean cheese, pepper, sumac and cayenee and combine.
When the dough is ready, divide into two equal sized balls. Keeping one covered, roll one into a 16 x 7 inch rectangle, top with a layer of provolone cheese, leaving a 1/2 inch border, and then top with half of the spinach mixture. If you are having trouble getting the challah to roll out, let it rest for a minute so the gluten can relax.
Roll the rectangle up tightly like a jelly roll starting from the long end. Then form a spiral to make a round mound, tucking the end under. Repeat with the other dough ball.
I like to bake each loaf on it's own cookie sheet because they spread. Carefully place the loaves on two parchment lined baking sheets, cover lightly with plastic wrap or a towel, and let it rise for another 45 minutes or so until it's light and fuffy looking (exact proofing timing for challah will depend on environmental conditions.)
Meanwhile, preheat oven to 350 degrees F. Whisk the last egg yolk with 1/2 tablespoon water and generously brush over challah. Repeat to have two coats. Bake two at a time for 30-35 minutes, or until golden brown and with an internal temperature of 190 degrees F, rotating pans halfway through. If the challot start to brown too fast, lightly cover with foil. Serve warm or room temperature!