In a mixing bowl, combine the cream cheese, shredded cheddar cheese, and shredded mozzarella cheese. Mix until well combined.
Add the sliced jalapenos to the cheese mixture and stir until evenly distributed.
Take two slices of sourdough bread and butter one side of each slice.
Place one slice, buttered side down, into a non-stick skillet over medium heat.
Spread half of the cheese and jalapeno mixture on the unbuttered side of the bread in the skillet.
Top with another slice of bread, buttered side up.
Cook for about 3-5 minutes or until the bottom slice is golden brown.
Carefully flip the sandwich using a spatula and cook the other side for an additional 3-5 minutes until golden and the cheese is melted.
Remove the sandwich from the skillet and let it cool for a minute before slicing.
Repeat the same process with the remaining ingredients to prepare the second sandwich.
Slice the sandwiches in half and serve hot.