Preheat the oven to 180°C (approximately 350°F). Grease a springform pan with butter and sprinkle with flour.
For the batter: Beat the butter until fluffy. Alternately stir in the sugar and eggs. Add the salt. Mix together the baking powder and flour then gradually stir into the batter with the milk just until combined. Transfer 1/2 to the prepared pan and smooth the top.
Rinse the apples, cut into quarters, remove the seeds and cut into thin slices. Toss with the lemon juice and arrange 1/2 in a fan shape over the batter. Cover with the remaining batter and arrange the remaining apple slices over top. Bake until golden brown, about 45 minutes.
Mix the Calvados with the powdered sugar, remove the cake from the oven and, while still hot, sprinkle with the Calvados. Let cool, loosen from the mold and serve.