Peel, core, slice, and dice the apples. Toss them with lemon juice.
Melt the butter in a 2-quart nonstick pot over medium to medium-low heat. Add the apples, toss to coat evenly, and cook for 5 minutes, stirring frequently.
Add the brown sugar, cinnamon, sea salt, and Calvados, stir well, and simmer for an additional 10 minutes, or until the apples are tender and the liquid has reduced.
In a liquid measuring cup, whisk the water and cornstarch until smooth, then stir into the apple mixture.
Simmer for an additional 2 minutes, stirring frequently, then remove from heat.