Fry the lardons or chopped rashers in a pan until crisp and then leave to dry on kitchen paper. Keep the pan.

Slice the runner beans into long thin strips, removing the ends and stringy sides. Boil in a pan for 2-3min until al denté. Be careful not to overcook.

Whisk the crème fraîche, lime juice, egg yolk, mustard and half the chopped chives together.

Put runner beans, carbonara sauce and bacon into the pan on a low heat and stir until sauce thickens. Be careful not to burn. Serve immediately and top woth remaining chives.