Ceanberry Upside Down Cake

Ingredients
For the topping:
1/2 stick butter (4 tablespoons)
3/4 cup plus packed light brown sugar
1 12-ounce bag cranberries (if using frozen, don't thaw them first)

For the cake:
1 1/2 cups all-purpose flour
1 1/2 teaspoons baking powder
1 teaspoon baking soda
1 teaspoon kosher salt (or 1/2 teaspoon table salt)
1 stick (1/2 cup) butter, softened
2/3 cup granulated sugar
1 teaspoon vanilla
1 teaspoon grated orange zest (from 1 large orange)
2 eggs
1/2 cup buttermilk
1/4 cup milk

Directions

1.      Heat the oven to 350ºF. Now begin with the topping. I prepare and bake this cake in a very well-seasoned 10-inch cast-iron skillet. If you're using a cake pan, then you will need to do the butter and brown sugar part in the oven, and you may want to line the pan with parchment first. For skillet-users: melt the butter over medium heat, then stir in the brown sugar and cook, stirring, for a minute or two. Spread the mixture out as best you can, and leave it to cool while you prepare the cake batter. Sift (or, hello lazy friend of mine, whisk) together the flour, baking powder, baking soda, and salt. Meanwhile, in an electric mixer, you are beating together the butter and sugar until they are very fluffy-stopping to scrape down the bowl if there's a dead spot down there, below the beater, like there is with mine. Add the vanilla, the orange zest, and the eggs, one at a time, beating well after each. With the mixer on low speed add the flour alternately with the buttermilk and milk, which you've sensibly mixed together in the measuring cup. Beat until just combined, or risk overbeating and baking something with the delicate texture of an anvil. Now pour your cleaned berries (I rub them dry in a clean dish towel) into the prepared pan, shake to even them out, and spoon the batter over them in large blobs which you will smooth and spread together very gently with a spatula so as not to disturb the berries which are, shhhh, already asleep at the bottom of the pan. Bake the cake in the middle of the oven until quite brown and done-looking, about 40-45 minutes, or until a tester comes out clean. Now -- this is important -- cool the cake in its skillet on a rack for exactly 15 minutes, then run a knife around the edge of the cake, then place a large plate over the pan with one hand while your other hand is busy having an oven mitt on it and holding the skillet's handle, invert the cake, holding skillet and plate tightly together and then removing the skillet with an optimistic flourish.