Add the pineapple juice, treacle, ketchup, Worcestershire sauce, garlic powder and smoked paprika into a small pan. Add a splash of the liquid from the jalapeño jar. Whisk together, and place over a medium high heat.

Mix the cornflour with 2 tbsp water to make a loose paste. Whisk into the sauce, whisking constantly as it thickens the sauce – it needs to bubble and boil in order to cook out the cornflour and stop it tasting like flour.