Place the tomato paste, chipotle pepper, adobo sauce, and molasses in a blender or food processor and purée until smooth.
Taste the pepper spread so you’ll know how spicy it is, and spread each slice of bread with as much of the pepper mixture as you’d like. We use about 1 tablespoon per slice.
On each of 4 slices of bread, place 1 1/4 slices of cheddar cheese, then place 2 to 3 tomato slices on the cheese. Top with a few thin rings of sliced red onion and a tablespoon of chopped cilantro. Place 1 1/4 more slices of cheese on each sandwich. Place another slice of bread, pepper spread side down, on top of each sandwich.
If you have a sandwich grill, heat the sandwiches following the manufacturer’s instructions until the bread is toasted and the cheese has begun to melt. If you don’t have one, place a large skillet or sauté pan over medium-high heat for 30 seconds. Put the sandwiches in the pan and weight them down with a clean, heavy pot. When the bread has begun to toast and brown, 1 to 2 minutes, flip the sandwiches over and toast the other side. Serve immediately.