This cabbage pie is very popular in Russian cuisine. Traditionally, it is made with a yeast puff pastry but normal puff pastry will work just fine. You can bake it as one big pie, or make small triangles called pirozhki.
Melt butter over medium-low heat; add chopped cabbage and cook for 30 minutes, until softened but not browned. Cool.
Preheat oven to 200 C / Gas 6.
Mix cooled cabbage with eggs and dill; season to taste with salt.
Place 1 sheet of puff pastry on a baking tray or arrange in a pie tin. Add cabbage filling, leaving some space around the edge. Cover with second sheet of puff pastry and pinch edges together. Glaze the top with beaten egg.
Bake in preheated oven for 40 to 45 minutes, or until golden brown. Serve warm.