In a pot over medium heat, melt the butter, then add the flour. Stir to combine.
Add the Sriracha and milk, stir to combine. Simmer the mix for approximately 5 minutes to allow it to slightly thicken.
Remove the mix from the heat, then add the cheddar cheese, garlic powder, salt, and cayenne pepper. Stir until the cheese is melted and the sauce is well combined.
Taste, and add more Sriracha or cayenne pepper to taste/heat preference. Serve.