Preheat oven to 220°C/425°F. Grease and line a large oven tray with baking paper.
Grate unpeeled apple; squeeze excess moisture from flesh. Combine mince, parmesan, breadcrumbs, grated apple, mustard, thyme and 1 lightly beaten egg in a medium bowl; season.
Lightly beat remaining egg in a small bowl. Place 1 sheet of pastry on a work surface. Place one-third of the filling mixture lengthways down one side of the pastry, 1.5cm (¾in) from the edge. Brush pastry edge with a little egg; roll to form a sausage roll. Trim and discard excess pastry. Repeat with remaining pastry and filling mixture and a little more egg. Cut each roll in half.
Place rolls, seam-side down, on lined tray; brush tops with egg and sprinkle with extra thyme.
Bake rolls for 25 minutes or until pastry is golden and rolls are cooked through. Serve with sriracha.
