Upside down cake with plum

Name: Upside down cake with plum
Prep time: 15 min
Cook time: 55 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 1/3 cup yellow cornmeal; 1 cup flour; 1 tsp baking powder; 1.4 tsp baking soda; ½ tsp salt; 1 stick butter (room temperature); 2/3 cup sugar; 2 eggs (room temperature); 2 tsp vanilla extract; 2 tbsp honey; 3/4 cups buttermilk ( room temperature); 4 tbsp butter (softened); 3 tbsp brown sugar; 2 cups plums (sliced (I used maybe three plums that I cut into eight slices each))