Preheat the oven to 350 degrees (or 325 if you’re using a dark pan).

Pour the melted butter into the bottom of a 13-by-9-inch baking pan. Sprinkle the brown sugar over the butter in an even layer.

Drain the pineapple rings, reserving the juice for the cake. Arrange the pineapple over the brown sugar and place a cherry in the center of each pineapple slice. Arrange additional cherries around the slices; lightly press the cherries and pineapple into the brown sugar.

Measure out 1 cup of the reserved pineapple juice (if you don’t have enough add a little water). Combine the juice, cake mix, vegetable oil, eggs, and vanilla (if using) in a large mixing bowl and beat with an electric mixer set to medium speed for 2 minutes, until batter is smooth.

Pour the batter into the pan and gently smooth the top. Tap the pan on the counter a couple of times to eliminate air bubbles, then bake 38 to 44 minutes, until a toothpick inserted into the center of the cake comes out clean. Remove from the oven and quickly run a knife around the edge of the pan.

Place a large serving platter or cutting board on top of the pan and flip them both over. Let the cake pan sit on the platter/cutting board for 5 minutes, then carefully remove. Cool cake for 30 minutes, then serve (topped with whipped cream if desired).

Cake will last loosely covered in the fridge for up to 2 days.