Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
Cut the jalapenos in half lengthwise and remove the seeds (if less heat is desired). Place them cut-side down on the baking sheet.
Roast the jalapenos in the oven for about 10-15 minutes or until the skins are blistered and slightly charred. Remove from the oven and let cool.
In a mixing bowl, combine the softened cream cheese, shredded cheddar cheese, and shredded mozzarella cheese. Mix well. Season with salt and pepper to taste.
Once the jalapenos are cool, chop them into small pieces and fold them into the cheese mixture.
Heat a skillet or frying pan over medium heat. Spread butter on one side of each slice of bread.
Place 4 slices of bread, buttered side down, in the skillet. Spoon a generous portion of the cheese and jalapeno mixture onto each slice.
Top with another slice of bread, buttered side up. Grill until the bread is golden brown and the cheese is melted, about 3-4 minutes on each side.
Remove from the skillet and let sit for a minute before slicing. Repeat with the remaining ingredients to make the next batch of sandwiches.
Serve warm and enjoy your Roasted Jalapeno Popper Grilled Cheese!