Preheat your oven to 350°F.

Make the bourbon caramel: Set your 10–12" cast iron skillet over medium-low heat. Melt 4 tablespoons of butter completely, then add the dark brown sugar and kosher salt. Stir until the sugar dissolves and the mixture bubbles gently, about 2–3 minutes. Pull the pan off the heat and carefully add the bourbon — it will sputter and sizzle. Stir to combine and tilt the pan to spread the caramel evenly across the bottom.

Arrange the pineapple: Pat the pineapple rings completely dry (excess moisture is the enemy of a clean flip). Arrange them over the caramel — one in the center, six around the edge. Tuck a cherry into each ring center if using. Set the skillet aside, off heat.

Mix the wet ingredients: In a large bowl, whisk together the cooled brown butter, granulated sugar, and dark brown sugar until combined. Add the eggs one at a time, whisking well after each. Stir in the vanilla extract, then the sour cream and milk. The batter should look smooth and glossy.

Add the dry ingredients: Sift the flour, baking powder, baking soda, and salt directly into the bowl. Fold with a rubber spatula until just combined — stop the moment you can't see any dry streaks. A few lumps are completely fine. Overmixing develops gluten and makes a tough cake.

Fill and bake: Pour the batter over the pineapple in the skillet, spreading gently to the edges without disturbing the fruit. Transfer to the oven and bake for 35–42 minutes, until the top is deep golden brown and a toothpick inserted in the center comes out clean.

The flip: Let the cake cool in the skillet for exactly 10 minutes — set a timer. No longer, or the caramel will begin to harden and stick to the pan. Run a thin knife around the edge. Place a large serving plate or cutting board firmly on top of the skillet, then flip in one confident, decisive motion. Leave the skillet resting on the cake for a full 60 seconds before lifting straight up — gravity does the work of releasing the caramel. While the caramel surface is still warm and tacky (within the first 2 minutes), scatter a light pinch of flaky sea salt across the top. The flakes will adhere just enough to stay put and deliver little pops of salinity in every bite.

Serve warm or at room temperature. A scoop of vanilla ice cream or a dollop of unsweetened whipped cream is the ideal accompaniment — the contrast of cold and the neutral fat helps cut through the caramel richness beautifully.