1.Make the chilli con carne: In a large frying pan, heat oil over high heat; cook onion, garlic, beef, chipotle chilli and cumin, stirring, for about 5 minutes, or until beef is browned. Stir in beans, tomatoes, stock and sugar; bring to the boil. Reduce heat to low; simmer, uncovered, for about 12 minutes or until thickened, stirring occasionally. Season to taste.
2.In a large saucepan of simmering water, cook frankfurters over medium heat for about 5 minutes, or until warmed through.
3.Spread buns with mustard. Top with frankfurters, chilli con carne, onion and cheese.
Chipotle chillies in adobo sauce are sold in small cans from delicatessens and specialist food stores; they have a medium-hot smoky taste. Any leftover chillies will keep with their sauce in a small screw-top jar in the fridge for up to 3 months. Substitute with a teaspoon of smoked paprika and a pinch of chilli powder. Do ahead: You can make the chilli con carne ahead of time; refrigerate, covered. Gently reheat before serving. You may need to add a little extra stock to moisten it.