Preheat the oven to 350°F (177°C) and generously butter a 10-ounce ramekin.
In a small bowl, melt the butter and stir in the brown sugar until combined.
Pour the mixture into the buttered 10-ounce ramekin. Place the pineapple slice on top and set the cherry in the center.
In a separate bowl, cream the softened butter and sugar. Mix in the egg yolk and vanilla until smooth.
Add the flour, baking powder, and salt, and stir until just combined. Stir in the milk until the batter is smooth.
Pour the batter over the fruit and bake for 30 minutes.
Let the cake cool for 15 minutes. Run a knife around the edges to loosen it. Place a plate over the ramekin, hold both together, and carefully flip. Lift off the ramekin, the cake should release onto the plate. Use oven mitts if the ramekin is still warm.
Notes
Butter the ramekin well: Helps the cake release easily after baking.
Neatly arrange the fruit: For a clean, attractive look when flipped.
Check for doneness: A toothpick should come out clean.
Cool before flipping: Let the cake sit for 10–15 minutes to set.
Serve warm: Best flavor and texture when served shortly after baking.
If doubling the recipe, use two 10-ounce ramekins or one 5x5-inch baking dish.