Preheat oven to 200°C/425°F.

Grate the onion into a bowl, reserving the juices. Add panko breadcrumbs and toss to wet.

Add beef, egg, garlic, stock cube, salt, pepper, and jalapeño to the onion mixture. Mix well with hands to combine.

Add both cheeses, crumble through the beef with fingers, then mix well.

Thaw puff pastry slightly. Divide the meat mixture into 2 equal logs. Roll in puff pastry and seal with egg white.

Cut each log in half. Cut 3 diagonal slashes on top of each sausage roll. Brush with egg yolk and sprinkle with sesame seeds.

Place sausage rolls on a paper-lined tray. Bake for 35 minutes, then transfer onto a rack and bake for a further 15 minutes until golden.

Cool on a rack for 5 minutes before serving with sauce.