In a large cold skillet, add the bacon. Turn the heat to medium and cook, flipping halfway through, until the bacon is crispy and browned, about 10 minutes. Transfer to a paper towel-lined plate to drain.
Assemble your grilled cheese sandwiches: smear 1 tablespoon of the jam on one side of each piece of bread. On the jam side of two of the slices of bread, layer half of the cheese, top each half with two to three slices of bacon, and then top with the remaining cheese. Close your sandwiches with the jam side facing down.
In the skillet, melt the butter. Cook the sandwiches over moderately-low heat, flipping once and adding more butter as needed, until the bread is golden brown and the cheese is gooey and melted, about 5 minutes per side. If needed, cover the skillet to help the cheese melt.
Slice the sandwiches on the diagonal, sprinkle with a little flaky sea salt, and serve right away.