Warm a medium sauce pan over medium heat. Add butter and melt. Once the butter us melted add flour and stir for about 30 seconds to cook.
Stir in salsa, green chillies and cook, stirring, until mixture is simmering.
Stir in sour cream.
Add grated cheese and continue stirring until cheese is completely melted.
Return mixture to a simmer, then lower heat to the lowest setting.
Garnish with toppings.
Transfer to a bowl if eating immediately or leave in the sauce pan over low heat until ready to serve.
Serve hot, surrounded with chips.