Method:

Combine the butter and sugar in a large mixing bowl and mix until the mixture lightens slightly and is well combined. Add the salt and vanilla and combine.
Add the eggs and whisk until the mixture becomes light in colour and fluffy in texture. Add the sour cream and whisk in.
Sift in the flour and baking powder before folding into the mixture using a silicone spatula to ensure every bit of the dry ingredients in combined with the wet ingredients.
Preheat the oven to 180C
Prepare the nectarines by using an oven proof pan coated with non-stick kitchen spray. Add the sugar to the pan place over a medium heat, allowing it to melt, swirling the pan when necessary instead of stirring.
Once the sugar takes on a light brown colour add the nectarines to the pan and, tightly packing them into the pan placing them cut ice facing up. Allow the nectarines to cook for about 1 minute or until they just begin to brown on the underside then remove from the heat.
Pour the batter into the pan ensuring that all the gaps are filled with the batter. Place the pan in the preheated oven and bake for 30-35 minutes or when a cake tester comes out clean after testing the cake. Let the cake rest for 5 minutes after taking it out the oven before covering it with a plate and carefully turning the pan upside down and removing to reveal the cooked nectarines.
Combine the creme fraiche with the vanilla and icing sugar and serve with the sliced cake.