Melt the butter in a large sauté pan or deep skillet over medium heat. Use instant pot for keeping cheese warm easily!
Add in the onion, garlic, jalapeño and salt and cook for 5 minutes, stirring occasionally, until the vegetables soften and become very fragrant.
Add in milk and cream cheese. Stir continuously until the cream cheese has melted and is mostly smooth, about 5 minutes.
Reduce the heat to low and add in the shredded cheeses in batches, stirring each batch into the mixture until it has completely melted before adding the next.
Remove the pan from the heat and stir in the salsa. Taste and add more if desired. Serve immediately with tortilla chips.
