Crack one of the eggs into a bowl. Add the cheddar, onion and peas and stir until everything is coated in the egg.
Unroll the puff pastry sheet. Cut in half longways, then into 5 pieces along the short edge so that you have 10 equal sized rectangles.
Place a spoonful of the filling on one half of each piece of pastry. Fold the other half over and press down all around with your thumb or the back of a fork to seal.
Beat the other egg in a bowl, then brush the egg over each puff.
Pop them on a baking tray, prick the top of each one with a fork and put in the oven for 20-25 minutes, or until puffed up and golden. Enjoy hot or cold!