rosemary plum upside-down cake

Somebody needs to invite me to brunch. This cake is so easy, I don't even need any notice. I can use any fruit and everything else that I need is already here. Let's do it.
It's baked in a cast iron pan, which for me, is already a qualifying aspect for greatness. The butter will help season your pan as the cake bakes so basically, you're welcome. The cake itself is not very sweet (perfect for breakfast) and the fruit transforms into a thick layer of caramelized fresh jam but not in a sticky way. It would be amazing with peaches, apples, pears, berries or mango... and I am having a hard time not making it with each just so I can flip the pan again.

Here is what you need: 1 stick (8 T Earth Balance), 1/2 C dark brown sugar, 2 t chopped rosemary leaves (very optional), 4 sliced plums, 1 C vegan milk (I am partial to almond these days), 1 T apple cider vinegar, Egg replacer for 2 eggs (your call, I used the powder), 1/2 C sugar, 2 C flour (whole wheat might be an interesting substitute here), 1 t baking soda, 1/4 t salt.

Preheat oven to 350. Grease your cast iron skillet with 1/2 the butter. Don't be stingy! Cover bottom of pan with brown sugar, herbs if using and a decorative assortment of sliced fruit.

In a small bowl, combine milk and vinegar. This will create a "buttermilk" effect in the time it takes you to mix everything else. Flour, baking soda and salt go in a large mixing bowl.
Combine remaining butter (melted) with egg replacer, sugar and "buttermilk" mixture until creamy. Add wet ingredients to dry ingredients and stir batter til smooth. Pour evenly over fruit. Bake until very brown on top- 50 minutes. Let cool 5 minutes. Run butter knife around edge of pan and nudge with spatula if necessary to flip the cake over. Say "Ooooooooooh!"

Suggested Cooking Jam: Diana Ross, Upside Down (obvs)