Lay out the slices of bread and spread butter on one side of each slice.
On the unbuttered side of four slices, layer the ingredients as follows: one slice of cheddar cheese, a few slices of turkey, spinach leaves, two slices of bacon, and another slice of cheddar cheese.
Top with the remaining slices of bread, butter side up.
Heat a skillet over medium heat and grill each sandwich until the bread is golden brown and the cheese is melted, about 3-4 minutes per side.
Remove from skillet, let cool slightly, and slice in half before serving.
Notes
For a spicier kick, add a dash of hot sauce inside the sandwich before grilling.