Melt the butter in a pan on the stove and add the jalapeno and onion.
Cook for 5 minutes or until tender, stirring often.
Add the garlic and cook for 30 seconds.
Add the flour and cook for a minute, stirring all the time.
Whisk in the Half & Half.
Bring the mixture to a simmer and gently cook for 3 minutes.
Turn the heat down low and add the cheese, little by little, whisking until it melts before adding more.
Next add the salt, tomatoes and cumin.
Adjust the seasoning if needed or add some milk or Half & Half if the dip is too thick.
Transfer into a serving bowl to serve.