Preheat the oven to 400.
Dice the onion and sauté in the olive oil until it's slightly browned
Put the raw, loose sausage in a bowl. Beat two of the eggs and add them to the bowl along with the cooked onions. Mix thoroughly.
Cut the puff pastry into six long strips. On a floured surface, roll them out until they're somewhat thinner.
Divide the sausage mixture into six portions and spoon it out into a long rows down the middle of each strip of puff pastry
Form the sausage mixture into a tidier strip, leaving a margin of dough on each side.
With a pastry brush, paint the dough margins on both sides.
Fold the pastry up over the sausage on both sides, to form a long roll.
Flip the roll over and lay it in a greased pan with the creased side down.
Cut each roll into six smaller sections. (You can make them whatever size you like, really.) Leave a little space in between rolls on the pan.
Brush each little roll with the rest of the beaten egg. Sprinkle with "everything" seasoning if you like.
Bake for 20 minutes until the sausage is cooked and the rolls are golden brown. Serve hot or cold.