Pre-heat the oven to 160°C/325°F. Grease a 10 inch tube pan generously with cooking spray and set aside.
Cream together the butter and sugar at high speed in a stand mixture until it’s fluffy and starting to look white, about 4-5 minutes, add cream cheese and mix for another minute.
Stir in the eggs, a little at a time, beating the mixture well between each addition. Sift in the flour and baking powder into the batter, and then add the, nutmeg, vanilla and rum
Stir well until everything is fully combined. Scrape down the sides of the mixing bowl.
Melt chocolate in a small bowl in the microwave, stirring frequently every 20-30 seconds. So that is doesn’t scorch or burn. It usually takes about 2 minutes.
Fold in the melted chocolate with about ⅓ of the cake batter. Mix well until fully incorporated.
Alternating spoon vanilla and chocolate layers into prepared pan to simulate a checkerboard.
With a large spoon, cut and twist through batters to obtain marbled effect. Tap the pan firmly to remove air pockets.
Bake cake until a tester inserted into the center comes out clean, 45–50minutes . Transfer to a wire rack. Let cake cool in pan for 10 minutes. Then remove and transfer to a wire rack.