Start by cutting the puff pastry sheet into 4 equal-sized strips.
In a small bowl, add the ketchup, the mayonnaise and mix.
Now, using a brush, spread this mixture over half of each pastry strip we cut earlier.
To make the filling, top each strip with 3 slices of smoked sausage, ½ slice of tomato and 25g of grated cheddar cheese.
Then, close the pastries by folding them over the fillings and to close them well, press the ends together with a fork.
Transfer them all to a baking tray lined with parchment paper and brush a beaten egg over all of them.
Add sesame seeds to taste and top each one with 25g of grated mozzarella cheese.
Take to a preheated oven at 200° C (400° F) and bake for 25 minutes.
Serve.