Prep the pan and oven. Preheat to 350°F (175°C). Grease a 9-inch round pan and, if you like, line the bottom with a parchment circle for easy release.
Make the caramel base. Melt 1/2 cup butter in a small saucepan over medium heat.
Stir in 3/4 cup brown sugar and cook 1–2 minutes until the sugar looks glossy and thick. Immediately pour into the pan and tilt to coat the bottom evenly.
Arrange the fruit. Lay pineapple rings over the caramel, snug but not overlapping too much. Tuck a cherry into the center of each ring and any gaps. Pat fruit dry first so the topping isn’t watery.
Whisk dry ingredients. In a bowl, whisk flour, baking powder, and salt.
Set aside.
Combine wet ingredients. In a measuring cup, whisk milk, sour cream, vanilla, and optional pineapple juice.
Cream the butter and sugars. In a large bowl, beat 1/2 cup softened butter with granulated sugar and 1/4 cup brown sugar until light and fluffy, about 2–3 minutes. This step builds structure and tenderness.
Add eggs. Beat in eggs one at a time, scraping the bowl. Mix until smooth and slightly thickened.
Bring it together. Add the dry ingredients in two additions, alternating with the milk mixture.
Start and end with the dry. Mix on low just until combined. Don’t overmix or the cake will turn dense.
Fill the pan. Spoon batter over the fruit and gently spread to the edges. The pan will be fairly full—this is normal.
Bake. Bake 40–50 minutes, until the top is golden and a toothpick inserted into the center comes out clean or with a few moist crumbs.
If the top browns too quickly, tent loosely with foil for the last 10 minutes.
Cool briefly, then invert. Let the cake rest on a rack for 10 minutes. Run a knife around the edge, place a serving plate over the pan, and invert carefully. Tap the bottom to release.
If any fruit sticks, lift it off and press back into place.
Serve warm or at room temperature. The glaze sets as it cools. Slice gently with a serrated knife to protect the fruit.