Step 1

Adjust oven rack to middle position and heat oven to 425 degrees. Cook bacon in 10-inch skillet over medium heat until crispy, 5 to 7 minutes. Using slotted spoon, transfer bacon to paper towel–lined plate. Measure out 1 tablespoon fat from skillet and add to melted butter; discard remaining fat. Combine cheddar, cream cheese, fresh jalapeños, jarred jalapeños, scallions, pepper, and bacon in bowl.

Step 2

Line rimmed baking sheet with foil. Brush 1 side of each slice of bread with melted butter mixture. Place 4 slices of bread, buttered side down, on prepared sheet. Divide cheddar mixture evenly among bread slices and spread into even layer. Top with remaining slices of bread, buttered side up.

Step 3

Bake sandwiches until golden brown on top, 6 to 8 minutes. Flip sandwiches and continue to bake until golden brown on second side and cheese is melted, 6 to 8 minutes longer. Let cool for 5 minutes. Cut sandwiches in half and serve.