Tear the phyllo sheets into small, irregular pieces, about 2 to 3 cm each, and spread them on a tray. Leave uncovered at room temperature for at least 3 hours, or overnight, so they dry out and turn brittle.

Heat the oven to 180 C / 350 F. Grease a 23 x 33 cm / 9 x 13-inch baking dish with oil or butter.

Whisk the eggs and sugar together in a large bowl until pale and slightly thick, about 2 minutes.

Add the yogurt, oil, orange zest, orange juice, vanilla, baking powder, salt, and cinnamon if using. Whisk until smooth.

Add the dried phyllo pieces to the batter and fold gently with a spatula until every piece is coated. Let it sit for 10 minutes so the phyllo starts soaking up the batter.

Pour the mixture into the prepared dish, spread it evenly, and press down lightly with the back of the spatula.

Bake for 40 to 45 minutes, until deep golden brown on top and a skewer inserted in the center comes out clean.

While the cake bakes, combine the syrup sugar, water, orange juice, cinnamon stick, and orange peel in the saucepan. Bring to a boil, then reduce heat and simmer for 8 to 10 minutes, until slightly thickened like thin honey.

Remove the cinnamon stick and orange peel from the syrup and discard them.

As soon as the cake comes out of the oven, ladle the warm syrup over it slowly and evenly, letting it soak in rather than pool on top.

Let the cake rest at room temperature for 30 minutes so it fully absorbs the syrup before you cut into it.

Cut into 12 squares and serve warm or at room temperature.