Melt butter in a pot over medium heat and add the flour. Stir to slightly toast the flour.
Add garlic and onion powder, along with the salt and pepper.
Add chicken stock once the flour looks slightly browned. Keep stirring and add jalapenos.
Take off heat once the sauce thickens. Cool for a few minutes and stir in the sour cream. Top with chives.
Notes
Just like most other sauces, this one tastes so much better after you refrigerate it for a few hours.
Heat can curdle sour cream, so make sure you stir it in a few minutes after you've taken the pot off heat.
You can also add a spoonful of cream cheese or some shredded cheese into the mix to get it another layer of flavor.
You can reduce or increase the amount of stock you're adding to adjust the consistency of the sauce to your liking. Sometimes, I like to use a splash of milk to get some extra richness.