Heat the butter in a large frying pan, add the pineapple, in batches if necessary, and cook for 1 minute on each side until golden. Sprinkle over the sugar and cook for a further 2 minutes until it starts to caramelize. Remove the pineapple from the pan.
Pour in the tequila and lime juice, bring to the boil and cook for 1 minute until the mixture starts to thicken. Return the pineapple to the pan and coat in the sauce.
Transfer to serving plates and drizzle over any remaining sauce. Serve with scoops of ice cream.