For the cake 

Preheat oven to 170C. Cream the butter and sugar until pale and thick. Beat in the egg, then gently fold in the sifted flour, salt and milk. Combine until you have a soft dough. Grease and line the bottom of a 26cm spring-form tin. Spoon the mixture into the tin and level it. Don't expect a high cake - even with the topping and filling, this cake is all about the custard and nuts and is fairly thin.

For the topping 

Grind the nuts until quite coarse. In a frying pan, gently heat the extra butter, sugar, milk and nuts together. Stir until the butter has melted and everything is combined. Remove from heat and stir in the honey. Allow to cool slightly then pour over the cake batter and bake for 30-35 minutes or until golden brown.

For the custard filling

In a small bowl, combine enough milk to dissolve the powder and make a liquid paste. Now combine the custard, milk and sugar in a small saucepan and cook, stirring, until it thickens and boils. Cook for another minute, remove from heat and allow to cool a little. Beat butter until creamy and when the custard has become lukewarm, whip it with the butter until combined and fluffy.

Note: The custard should not be too warm as it will melt the butter.

To serve 

When the cake has cooled, slice through the middle and fill with the custard. Put back together and serve.

This cake, minus the custard filling, freezes well. Simply freeze in two pieces with a layer of greaseproof paper between each layer. Then thaw and make the filling on the day.