Preheat the oven to 220C / 200C fan.
Unwrap the puff pastry and lay it flat on a floured worktop. With a long edge toward you, spread 1 tablespoon of pesto on the right hand half, the crumble over the Castello Tickler Extra Mature Cheddar. Fold the left hand side of the pastry over, like closing a book, then dust with flour and roll out into a rectangle the same size as it started.
Turn the pastry so a short edge is toward you. Using a pizza cutter or sharp knife, cut across the top third of the pastry so that the bottom is a perfect square. Then cut the bottom piece into four squares.
Twists: cut the top third of the pastry into 3 long strips. Twist each over a few times to shape the twist then place on a baking sheet.
Plaits: take a square of pastry and spread a thin line of pesto down the centre, leaving a small space at the top and bottom. Cut horizontal lines, spaced 1 cm apart, coming from the pesto outwards. Plait the pastry strands over the filling and seal at the top and bottom with your fingers.
Diamonds: turn a square of pastry so that you have a diamond shape facing you. Lightly fold the diamond so the bottom point meets the top point. Make two incisions in the pastry, 2cm in from the outside, in a diamond shape, but make sure they do not meet at the top. Unfold the pastry. Fold the top diamond down and the bottom diamond up so you are left with a smaller diamond in the centre and two points coming out of either side. Spread pesto on top of the flat diamond in the centre and top with a few extra pieces of cheese.
Star: take a square of pastry and cut lines at 45 degrees in each corner, but make sure they don’t meet in the middle, so that you have 4 diamond-ish shapes in the piece of pastry. Fold one corner into the middle, followed by the same corner of the diamond-ish shape next to it, and repeat with the 3rd and 4th sections. You will be left with something that looks like a wind spinner. Place some pesto in the centre and top with a few extra pieces of cheese.
Square: fold all of the corners of a pastry square nearty into the centre of the pastry, stopping just short of the centre. Place a spoonful of pesto in the centre and top with extra cheese.
Beat the egg and milk then use it to egg wash the pastries, avoiding the edges of the pastry so that the puff pastry can still rise. Bake in the hot oven for 10 minutes, then egg wash again and bake for another 5 minutes until golden brown. Cool on a wire rack then crumble over extra Castello Tickler Extra Mature Cheddar before serving.