Melt the butter in a pan before adding the chopped onion, garlic and mixed herbs. Sauté gently for 5 minutes until softened. Add the cider and cook for a further 4 – 5 minutes until the liquid has evaporated. Set the onion mixture aside to cool.
Sprinkle the breadcrumbs and cheese into the onion mixture before combining all the ingredients with 1 egg. Set aside for 5 minutes for the breadcrumbs to absorb any excess moisture. Season with salt and pepper. (If you mixture is still a little wet, sprinkle in a little extra bread crumb).
Preheat the oven to 180C/gas 4. Roll out the pastry on a lightly floured surface and divide the pastry sheet lengthways to form two long rectangles. Divide the cheese and onion mixture into two.
Form a sausage shape of mixture down the centre of each rectangle, distributing evenly. Lightly whisk the second egg in a bowl and using a pastry brush, egg wash the pastry on one side of the mixture. Fold the pastry over the top of mixture and stick to the egg-washed side to seal. Using a fork, press the pastry together to fully seal. Repeat with the second pastry rectangle.
Brush the rolls with a little more egg wash before dividing each roll equally into 12 to form 24 mini rolls. Sprinkle with the nigella seeds and place on a lined baking tray.
Bake for 15 – 20 minutes until the rolls have puffed up and turned golden.