Beat the eggs and add the crumbled feta cheese to them. Spread out the phyllo pastry sheets, smear each with melted butter, distribute spinach and the feta cheese/egg mixture onto each, all over it.
Start folding up the sheets along their length, have the width of each burek be about 3″ (8 cm). Transfer the rolled up burek to the oven's tray, repeat for the other sheets. If you'd like less filling you can roll up 2 sheets with it instead of 1.
Smear the bureks with butter prior to baking. Bake in a preheated oven to a golden crisp.