Place the butter and a tablespoon of the water into a sauté pan and bring over medium heat until butter is melted. Add the sliced apples and stir to coat with the butter. Cook uncovered, stirring occasionally for 4-5 minutes to soften the apples. In a small bowl, stir together the cornstarch and water until combined. Add this mixture to the apples along with the brown sugar and cinnamon. Stir until well combined. Cover the pan and reduce the heat to low. Simmer for 3-4 minutes until the apples are tender and the sauce is thickened.