Medium low heat melt butter add Serrano and jalapeño and white onion, after about 5 mins add 2 big cloves minced garlic, whisk in equal amount flour to butter to make a roux and then whisk in some milk keep whisking until thickened up. Then add diced tomatoes and cilantro, keep mixing, drop heat to lowest possible and then start stirring in small ha drums of shredded cheese, I used an 8 oz bag fine grated "Mexican blend and a block of extra sharp cheddar that I grated finely" add cheese slowly stirring until cheese fully mixed before adding next. Add a lot of cheese. Once done throw in some sour creme or creme fraich or a Mexican crema and stir, salt, cumin and chili powder to taste and serve it up. Best queso I've ever had and super fun way to learn I had no idea how much chemistry it would require to make "queso" with all real cheese but it is so delicious! Serve with tortilla chips and pico!!