1. Preheat oven to 160C / 140C fan / Gas 3 (320F). Grease a 20cm loose-bottomed round cake tin, line the base with parchment, and place a foil-lined tray on the shelf below.

2. Make the toffee sauce: melt butter, muscovado sugar, and double cream in a small saucepan over low heat, stirring for about 2 minutes until golden and smooth. Set aside to cool slightly.

3. Beat soft butter and granulated sugar with an electric mixer until pale and fluffy, about 3-4 minutes.

4. Gradually add the beaten eggs a little at a time, adding a spoonful of flour after each addition to prevent curdling.

5. Beat in vanilla extract, then fold in the remaining flour, ground almonds, and baking powder until just combined.

6. Spoon half the batter into the prepared tin and spread evenly. Layer half the apple slices on top, then spoon over half the toffee sauce.

7. Spread remaining batter over the top, arrange remaining apple slices, then spoon over most of the remaining toffee sauce. Reserve a little sauce for finishing.

8. Bake for 1 hour to 1 hour 10 minutes until a skewer comes out clean. Cover loosely with foil if the top browns too quickly.

9. Rest in the tin for at least 45 minutes before unmoulding.

10. Warm the reserved toffee sauce and drizzle over the top before serving.