Combine cinnamon and sugar in a small bowl.
Lightly toast the bread until just crisp and warm. Immediately spread both sides of each slice of toast with butter and generously sprinkle with some cinnamon-sugar.
Note: you will likely have extra cinnamon-sugar.
Heat a skillet over medium heat. Add the chocolate to one side of two slices of toast, then place the second slice on top. Grill sandwiches in the skillet, in batches if necessary, for 1-2 minute per side or until the chocolate is melted. Serve immediately.
Recipe adapted from: www.halfbakedharvest.com