Preheat the oven to 350ºF (180ºC). Lightly butter a 9-inch (23-cm) round cake tin. Line the buttered tin with a parchment paper circle cut to fit.
Make The Apple Topping
Peel and core the apples. Slice them into ⅛-inch (3-mm) thick wedges.
Pour the melted butter into the prepared cake tin and swirl it around to evenly coat the bottom of the tin. Sprinkle the brown sugar over the melted butter. Arrange the apple slices however you like on top of the brown sugar. Set aside.
Make The Cake Batter
Whisk together the spelt flour, chai spice, baking powder and salt.
In another bowl, whisk together the melted butter, sugar, eggs, milk, and vanilla together until smooth.
Add the egg mixture to the flour mixture. Gently fold everything together until the flour is just mixed in. A few small streaks of dry flour in the batter are ok.
Gently spoon the cake batter over the sliced apples in the tin so as not to disturb the pattern you've created with the apple wedges. Lightly smooth the top of cake batter with an offset spatula or butter knife.
Place the cake in the oven and bake it for 30 to 33 minutes, or until the top is golden and lightly springs back when touched with the tip of your finger.
Transfer the cake to a wire rack to cool for 15 minutes then turn it out onto a large plate or serving platter. Serve the chai cake warm or cold, plain or with a dollop of whipped cream. A snowy dusting of powdered sugar once cooled is also a pretty touch.
Notes
You can bake the chai cake in an 8-inch (20-cm) round pan if that's all you have, however, the baking time will vary. A good way to check for doneness in a cake or loaf is to insert a digital thermometer in the middle of the cake and wait for a read of 200-205ºF (93-96ºC).For a less dense cake, don't melt the butter for the cake. Instead, use a hand or stand mixer and beat it with the sugar until pale and fluffy, about 10 minutes.
SUBSTITUTIONS
All-purpose flour can be substituted for the spelt flour.Cinnamon can be used instead of chai spice.