Remove the silver skin from the tenderloin. Very carefully remove and discard the seeds from the serrano chilis and finely chop them. Blanch the tomatoes in boiling water for 2 minutes - with a slotted spoon, remove and cool - then peel off skin and discard the seeds. Wash, dry and finely chop the cilantro. Cube the meat into 1 inch cubes. Chop the yolk of the egg into a crumb mixture.