Heat oven to 375º F.
Butter a 9-inch square pan.
In a saucepan, heat the milk, sugar, butter, and salt until small bubbles form. In a bowl, whisk together the eggs, then add the warm milk mixture in a slow stream, whisking constantly.
Layer the square pan with the bread. Top with the pears. Pour the milk-egg mixture into the baking pan and sprinkle with the cinnamon.
Bake until golden, about 35 minutes. Top with the Cheddar, if desired, and bake until the cheese is melted, 5 to 10 minutes. Serve warm.