• Preheat the oven to 170°C/Gas Mark 3.
• Grease and line a 25cm square shallow cake tin.
• In a mixing bowl, whisk the eggs, vanilla extract, and light soft brown sugar using an electric mixer on medium to high speed for about 5 minutes.
• The mixture should become pale, increase in volume, and be thick enough to leave a trail when dropped from the whisk.
• Gently melt the unsalted butter in a small pan.
• Fold the melted butter into the whisked batter using a large metal spoon, taking care not to deflate the mixture.
• Sift the plain flour, ground cinnamon, and baking powder together.
• Add the sultanas and toss to coat them in the flour mixture, which helps prevent them from sinking to the bottom of the cake.
• Gradually fold the flour mixture into the batter, 2 tablespoons at a time, followed by the milk.

Assemble the Cake:

• Transfer the cake batter into the prepared tin and level the surface with a spatula.
• Arrange the thinly sliced apples on top of the batter in a neat, overlapping pattern.
• Sprinkle the apples with the demerara sugar for added sweetness and crunch.

Bake the Cake:

• Bake the cake in the preheated oven for 20–25 minutes, or until the sponge is golden brown and the apples are lightly colored.
• Remove from the oven and allow the cake to cool in the tin.

Prepare the Icing:

• In a small bowl, whisk the icing sugar with enough Calvados or brandy to create a translucent icing.
• While the cake is still warm, brush the icing over the top.

Decorate the Cake:

• Arrange the toasted flaked almonds around the edge of the cake.
• Dust the cake lightly with icing sugar before serving.