Warm 3 tablespoons of the olive oil with the rosemary in a pan over a low heat for 5 minutes, take off the heat and let it infuse for 10 minutes. Remove and reserve the rosemary to use later.
Barbecue or grill the smoked back bacon until crisp. Chop finely.
Take 2 squares of foil (about 60 x 35cm), add the remaining oil and 75g popping corn to each one. Fold into loose parcels, sealing the edges. Give them a shake, then put on the coolest part of the barbecue for 5-10 minutes until the popping stops.
Tip the popcorn into a bowl, mix in the bacon and remaining rosemary oil. Sprinkle with chilli flakes and garnish with the rosemary sprigs.