Place diced apples evenly on the bottom of a 9×9-inch baking dish.
In a small bowl, whisk together flour, baking soda, salt and spices.
In a large bowl, whisk together 1/4 cup of melted butter and 1/4 cup of brown sugar until smooth. Beat in egg and vanilla extract, followed by maple syrup. Whisk in half of the flour mixture, followed by 1/2 cup of apple cider. Whisk in remaining flour mixture until no streaks of dry ingredients remain. Pour over apples and spread into an even layer.
Sprinkle batter with remaining brown sugar. Pour remaining 1/4 cup of melted butter and 3/4 cup apple cider over the top of the cake. Do not mix.
Bake cake for 35-40 minutes, until cake is set and deep golden brown at the edges, and filling is bubbling. Cool for 15 minutes before serving with a scoop of ice cream or a splash of warmed cream!