Set the oven to preheat at 350°F (177°C).

Begin by preparing the topping. Pour the melted butter into a 9-inch round baking pan or pie dish with a depth of at least 2 inches (ungreased). Evenly distribute the brown sugar over the melted butter. Pat the pineapple slices and cherries dry using a clean cloth or paper towel to remove excess moisture. Place approximately 6–7 pineapple rings in the pan, arranging them in a single layer over the sugar. Add the maraschino cherries to the center of each ring and fill any gaps decoratively. If desired, halve a few pineapple slices and position them along the sides of the pan. Refrigerate the arranged topping briefly while preparing the cake batter.

In a medium bowl, whisk together the cake flour, salt, baking powder, and baking soda. Set the dry mixture aside.

Using an electric mixer with a paddle or whisk attachment, cream the softened butter on high speed for about one minute until smooth. Add in the granulated sugar and beat on high for another minute, scraping down the sides of the bowl as needed. Continue mixing at high speed while incorporating the egg whites, followed by the sour cream and vanilla extract. Scrape the bowl again to ensure even mixing.

Reduce mixer speed to low. Gradually incorporate the prepared dry ingredients while simultaneously pouring in the pineapple juice and milk. Continue mixing just until all ingredients are fully blended. Avoid overmixing. If necessary, use a whisk to gently combine any remaining lumps by hand. The final batter should be somewhat thick.

Retrieve the chilled pan with the topping from the refrigerator. Pour the batter over the fruit, spreading it gently to cover evenly.

Bake the cake for 43 to 48 minutes. To prevent excessive browning, loosely tent the top with aluminum foil midway through baking. The cake is ready when a toothpick inserted in the center comes out mostly clean, with a few moist crumbs.

Once removed from the oven, allow the cake to cool in the pan on a wire rack for 20 minutes. Invert onto a serving platter or cake stand while still warm. Some topping juices may spill over the sides, which is expected. While the cake can be served warm, it will yield neater slices if completely cooled at room temperature. Avoid refrigerating the cake to hasten cooling, as it may become dense in texture.

Wrap any leftover slices and store in the refrigerator for up to 3 days or freeze individual portions for up to 3 months. Thaw at ambient temperature prior to serving. Whole cake freezing is not advised, as the decorative topping may not retain its visual appeal after thawing.