Preheat the oven to 180°C (350F), Gas mark 4. Peel the apples and cut each one in half, scooping out the core, then toss in the lemon juice to prevent them from going brown. Reserve the apple trimmings.
Smear the butter all over the bottom of large ovenproof frying pans, each with a bottom diameter of 23cm. Sprinkle over the caster sugar. Drain off the apples, reserving the lemon juice and arrange the apple halves on the sugar in a tight layer. Drizzle one tablespoon of the reserved lemon juice over each one. Cook over a high heat for 7-10 minutes until caramelised and the colour of fudge. Remove from the heat and leave to cool a little, then fill each each apple half with a pecan or walnut.
Meanwhile, make the sponge. Place the butter and caster sugar in a bowl and cream until light and fluffy. Whisk in the spices and then beat in the eggs, a little at a time. Sift in the flour, cornmeal and baking powder with a pinch of salt. Fold in a third of the flour mixture and then fold in a third of the milk. Repeat until all of the ingredients have been used up. Spread the sponge mixture in an oven layer over the apples and bake for 35 minutes until the sponges are well risen and golden brown.
To make the caramel syrup, place the sugar in a pan with the water and allow to caramelise undisturbed. Pour in the cider a little at a time, stirring continuously with a wooden spoon and being careful it doesn’t splutter and burn you. Add the reserved apple trimmings and simmer gently for 20 minutes to allow the flavours to combine. Strain through a fine sieve into a clean pan and set the apple caramel syrup aside until needed.
Remove the cooked apple upside down cakes from the oven and leave them at room temperature to cool and settle for at least 20 minutes. This will allow the sponge to soak up all the excess juices. Loosen each one around the edges with a palette knife and then turn out on to a flat plate, putting any dislodged apples or pecan nuts back in place.
To make the lemon mascarpone cream. Place the mascarpone in a bowl with the lemon rind and juice. Add the sugar and beat until well combined. Fold in the cream and then cover with cling film and chill until needed.
When ready to serve, heat the apple caramel syrup. Cut the apple upside down tart into slices and arrange on warmed serving plates. Add a large quenelle of the lemon mascarpone cream to each one and serve at once. The remainder of the apple caramel syrup can be put in a small jug and put on the table so that everyone can help themselves.