Preheat your oven to 180ºC/160ºC fan and line a 12 hole muffin tray with large cupcake cases or baking cups.

Peel and core the apples, then cube them into about 1 cm pieces. Mix the apple pieces with 25 g of light brown sugar and set aside.

For the crumble, rub together the sugar, plain flour, and unsalted butter until the mixture resembles bread crumbs, then set aside.

Beat the unsalted butter with the light brown sugar until light and fluffy. Add in the self raising flour, eggs, and ground cinnamon, and beat until smooth. Fold in the apple mixture and spoon into the cupcake cases.

Sprinkle a layer of the crumble mixture (about 1/2 cm worth) on top of each cupcake and bake for 20-25 minutes or until baked through.

Transfer the baked cupcakes to a cooling rack. Bake the spare crumble mixture on a baking tray for 15-20 minutes until lightly colored, then let it cool.

For the buttercream, beat the unsalted butter until light and supple. Gradually add in the icing sugar, mixing fully after each addition. Then, add ground cinnamon, vanilla extract, and 1-2 tablespoons of boiling water; beat until light and fluffy.

Pipe the buttercream onto the cooled cupcakes using a 2D closed star piping tip. Top with the cooked crumble mixture, an extra sprinkle of cinnamon, and enjoy.