Preheat the oven to 350 degrees.
Spray a 9-inch springform pan with cooking spray and set aside.
In a small bowl combine the flour, baking powder, and ¼ tsp. salt.
In the bowl of a mixer, combine the butter and the sugar. Beat until creamy.
Add the eggs, one at a time, beating until fully incorporated. Add the vanilla and rum, if using.
Add the flour mixture and mix just until the flour is fully incorporated.
Spoon batter into prepared pan (it will be thick!) spreading evenly. Lay the nectarine slices side by side along the edge of the pan in a decorative pattern.
Sprinkle the top of the cake with the brown sugar and crystallized ginger. Bake for 35 - 40 minutes or until a tester inserted into the center of the cake comes out clean.
Let cool and brush the fruit with the apricot jam if desired.