Wash, peel, and slice the nectarines. Add to a pot.
Add 2 Tbsp butter, white sugar, brown sugar (2 Tbsp each), and jam to the pot. Stir on medium-low heat for about 10 minutes until everything is well combined and the nectarines soften slightly.
In a bowl, melt 2 Tbsp butter. Add egg, milk, brown sugar, white sugar, vanilla, salt, baking powder, flour, nutmeg, cinnamon. Whisk thoroughly.
In a medium-sized baking dish (8-9 inch pan) add your batter and then your nectarines mixture on top. Smoothen out into an even layer. Note - you can easily double this recipe to fit into a 13-inch dish!
Cover dish with aluminum foil. Bake at 375 F for about an hour. Or until batter has set into a cake.