Grease and base line a 20cm (8 in) loose-bottomed cake tin.
First make your toffee sauce by melting all the ingredients together in a pan over a low heat and stirring and bubbling until golden, about 2 minutes. Set aside to cool.
Put the butter and sugar in the bowl of an electric mixer and cream together until pale.
Gradually add the beaten eggs, adding a large spoonful of flour after each to stop the mixture curdling.
Once the eggs are combined, beat in the vanilla extract, then add the remaining flour, ground almonds and baking powder. Fold in well.
Pour half the mixture into your prepared tin and spread in an even layer.
Arrange half the apple slices in a swirled layer, then spoon over half the toffee sauce. Repeat with the remaining cake mixture, apples and toffee sauce (leave a bit of toffee sauce for final drizzling, if you can).
Bake in the oven for 1 hour - 1 hour 10 minutes (check for doneness with a skewer after 1 hour).
The cake will rise up during baking and can drip good over the edge, so place a foil-lined tray underneath to catch any toffee drips.
Remove from the oven and leave to cool in the tin for at least 45 minutes before unmoulding.
Drizzle with the remaining toffee sauce and serve warm with ice cream or cold with hot tea.
Sophie Thompson's toffee apple cake https://www.amummytoo.co.uk/sophie-thompsons-oozily-delicious-toffee-apple-cake/