Preheat oven to 350 degrees F. Melt
butter over low heat and saute onion
until translucent. Mix in rice
, mushrooms, dill, and lemon juice
and let cool.
Lay out puff pastry
, place rice mixture over half of pastry and place salmon on top. Season with salt and pepper, and cover with eggs
. Fold over pastry and seal with beaten egg.
Crimp the edges of the kulebyaka. Brush with egg and poke a couple of holes in the pastry to let out steam. Bake for about 30 minutes until pastry is golden brown. Let cool and serve.