Roughly chop the candied jalapeños and spring onion before adding to a food processor to blitz.
Melt the butter in a saucepan then stir in the flour, mixing until a roux forms. Meanwhile heat the milk in another saucepan until the edges begin to bubble.
Gradually pour the milk into the roux while whisking. Cook for 5 minutes until the sauce thickens.
Add in the grated cheese along with the jalapeños and spring onions. Stir until all the cheese has melted. Season to taste.
Serve over a steak in a ciabatta sandwich.