Preheat your oven to 325 degrees Fahrenheit. Generously butter a 9 by 3-inch cake pan and line its bottom and sides with parchment paper to ensure easy removal.

Place the pineapple slices on layers of paper towels and press gently with another towel to absorb excess liquid. Repeat this drying step with the maraschino cherries.

Whisk together the cake flour, baking powder, nutmeg, and kosher salt in a large bowl until well combined and fragrant.

In a separate bowl, beat room temperature butter, avocado oil, sugar, and brown sugar using an electric mixer for about 2 minutes until the mixture is fluffy and light in color. Then add the eggs, vanilla extract, rum extract, pineapple emulsion if using, and the well-drained crushed pineapple, mixing for about 1 more minute.

Add half of the dry dry ingredients to the wet mixture and blend gently. Then stir in the buttermilk, pineapple juice, and maraschino cherry juice until well incorporated. Add the remaining dry ingredients and stir to combine.

Pour the melted butter evenly into the prepared cake pan and sprinkle the brown sugar over it. Lay the pineapple rings on top of the sugar-butter layer and place maraschino cherries in the center of each ring and between them. Cut the last three pineapple slices in half to place along the pan edges.

Pour the cake batter carefully over the arranged fruit, smoothing out the top without disturbing the fruit placement.

Bake for about 50 to 60 minutes until the cake is golden and a toothpick inserted into the center comes out with a few moist crumbs.

Let the cake cool in the pan for 8 to 10 minutes. If a dome has formed atop the cake, trim it flat before inverting onto a wire rack. This helps prevent cracking and keeps the cake's surface even.