While the cake is cooling, peel and core the apples and cut into 2/3-inch slices.
Place a large non-stick saute pan over high heat and once hot add about half of the apples.
Sear for 2 minutes, turning regularly until they are a nice golden color.
Remove from the pan, wipe it clean and repeat with the remaining apples.
Add these to the first batch and return the pan to medium heat.
Place the butter in the pan and, once melted, add the sugar, vanilla pod and lemon peel.
Return the apples to the pan, stir well to coat, and cook for 5 minutes, until the apples are soft but still holding their shape.
Pour in the brandy, lemon juice and salt and reduce for 3 minutes over medium-high heat, until the sauce is thick but not caramelized.
Spoon some of the warmed apples over each portion of cake and add a spoonful of crème fraîche.