Preheat the broiler and set a rack close to the broiler.
Combine the sugar and cinnamon in a small bowl.
Put the bread on a sheet pan and toast the bread lightly on both sides under the broiler. When the bread is hot, spread each piece with 1 teaspoon butter. Sprinkle the cinnamon sugar equally among the slices of toast. Top with equal quantities of the chocolate chips. Finally, lay 1/4 cup of the mini marshmallows on each slice.
Place under the broiler and broil just until the marshmallows are golden brown, watching them so they don’t burn, about 1 minute. Serve immediately.