Melt the butter in a pot over medium-low heat
Sprinkle flour slowly into melted butter, whisking constantly
Add salt, garlic powder, onion powder, and pepper.
Continue whisking until flour is incorporated and the mixture resembled a paste
Slowly pour in milk while whisking.
Whisk in buttermilk.
Bring to a simmer, whisking constantly.
Add cubed Velveeta and continue stirring with a large spoon, until Velveeta is melted.
Stir in jalapenos, onion, and tomatoes.
Cook additional 2-3 minutes or until heated through.
Serve warm.