In a microwavable bowl, place the cream cheese block and pour enough salsa over it to cover the block completely. The more salsa, the "soupier" your dip will be.
Heat in the microwave for 1 minute on high, until the cheese has melted.
Add the chopped jalapeño (or serrano), and stir to combine all ingredients.
Top with cilantro leaves if desired.
Notes
You can opt for an even hotter fresh chili pepper if you want your dip to be the spiciest possible.